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v2.32.0-rc1
git/compat/obstack.h
Jeff King cf82bff73f obstack: avoid computing offsets from NULL pointer 
As with the previous two commits, UBSan with clang-11 complains about
computing offsets from a NULL pointer. The failures in t4013 (and
elsewhere) look like this:

  kwset.c:102:23: runtime error: applying non-zero offset 107820859019600 to null pointer
  ...
  not ok 79 - git log -SF master # magic is (not used)

That line is not enlightening:

  ... = obstack_alloc(&kwset->obstack, sizeof (struct trie));

because obstack is implemented almost entirely in macros, and the actual
problem is five macros deep (I temporarily converted them to inline
functions to get better compiler errors, which was tedious but worked
reasonably well).

The actual problem is in these pointer-alignment macros:

  /* If B is the base of an object addressed by P, return the result of
     aligning P to the next multiple of A + 1.  B and P must be of type
     char *.  A + 1 must be a power of 2.  */

  #define __BPTR_ALIGN(B, P, A) ((B) + (((P) - (B) + (A)) & ~(A)))

  /* Similar to _BPTR_ALIGN (B, P, A), except optimize the common case
     where pointers can be converted to integers, aligned as integers,
     and converted back again.  If PTR_INT_TYPE is narrower than a
     pointer (e.g., the AS/400), play it safe and compute the alignment
     relative to B.  Otherwise, use the faster strategy of computing the
     alignment relative to 0.  */

  #define __PTR_ALIGN(B, P, A)                                                \
    __BPTR_ALIGN (sizeof (PTR_INT_TYPE) < sizeof (void *) ? (B) : (char *) 0, \
                  P, A)

If we have a sufficiently-large integer pointer type, then we do the
computation using a NULL pointer constant. That turns __BPTR_ALIGN()
into something like:

  NULL + (P - NULL + A) & ~A

and UBSan is complaining about adding the full value of P to that
initial NULL. We can fix this by doing our math as an integer type, and
then casting the result back to a pointer. The problem case only happens
when we know that the integer type is large enough, so there should be
no issue with truncation.

Another option would be just simplify out all the 0's from
__BPTR_ALIGN() for the NULL-pointer case. That probably wouldn't work
for a platform where the NULL pointer isn't all-zeroes, but Git already
wouldn't work on such a platform (due to our use of memset to set
pointers in structs to NULL). But I tried here to keep as close to the
original as possible.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-01-28 23:13:25 -08:00

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/* obstack.h - object stack macros
Copyright (C) 1988-1994,1996-1999,2003,2004,2005,2009
Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* Summary:
All the apparent functions defined here are macros. The idea
is that you would use these pre-tested macros to solve a
very specific set of problems, and they would run fast.
Caution: no side-effects in arguments please!! They may be
evaluated MANY times!!
These macros operate a stack of objects. Each object starts life
small, and may grow to maturity. (Consider building a word syllable
by syllable.) An object can move while it is growing. Once it has
been "finished" it never changes address again. So the "top of the
stack" is typically an immature growing object, while the rest of the
stack is of mature, fixed size and fixed address objects.
These routines grab large chunks of memory, using a function you
supply, called `obstack_chunk_alloc'. On occasion, they free chunks,
by calling `obstack_chunk_free'. You must define them and declare
them before using any obstack macros.
Each independent stack is represented by a `struct obstack'.
Each of the obstack macros expects a pointer to such a structure
as the first argument.
One motivation for this package is the problem of growing char strings
in symbol tables. Unless you are "fascist pig with a read-only mind"
--Gosper's immortal quote from HAKMEM item 154, out of context--you
would not like to put any arbitrary upper limit on the length of your
symbols.
In practice this often means you will build many short symbols and a
few long symbols. At the time you are reading a symbol you don't know
how long it is. One traditional method is to read a symbol into a
buffer, realloc()ating the buffer every time you try to read a symbol
that is longer than the buffer. This is beaut, but you still will
want to copy the symbol from the buffer to a more permanent
symbol-table entry say about half the time.
With obstacks, you can work differently. Use one obstack for all symbol
names. As you read a symbol, grow the name in the obstack gradually.
When the name is complete, finalize it. Then, if the symbol exists already,
free the newly read name.
The way we do this is to take a large chunk, allocating memory from
low addresses. When you want to build a symbol in the chunk you just
add chars above the current "high water mark" in the chunk. When you
have finished adding chars, because you got to the end of the symbol,
you know how long the chars are, and you can create a new object.
Mostly the chars will not burst over the highest address of the chunk,
because you would typically expect a chunk to be (say) 100 times as
long as an average object.
In case that isn't clear, when we have enough chars to make up
the object, THEY ARE ALREADY CONTIGUOUS IN THE CHUNK (guaranteed)
so we just point to it where it lies. No moving of chars is
needed and this is the second win: potentially long strings need
never be explicitly shuffled. Once an object is formed, it does not
change its address during its lifetime.
When the chars burst over a chunk boundary, we allocate a larger
chunk, and then copy the partly formed object from the end of the old
chunk to the beginning of the new larger chunk. We then carry on
accrediting characters to the end of the object as we normally would.
A special macro is provided to add a single char at a time to a
growing object. This allows the use of register variables, which
break the ordinary 'growth' macro.
Summary:
We allocate large chunks.
We carve out one object at a time from the current chunk.
Once carved, an object never moves.
We are free to append data of any size to the currently
growing object.
Exactly one object is growing in an obstack at any one time.
You can run one obstack per control block.
You may have as many control blocks as you dare.
Because of the way we do it, you can `unwind' an obstack
back to a previous state. (You may remove objects much
as you would with a stack.)
*/
/* Don't do the contents of this file more than once. */
#ifndef _OBSTACK_H
#define _OBSTACK_H 1
#ifdef __cplusplus
extern "C" {
#endif
/* We need the type of a pointer subtraction. If __PTRDIFF_TYPE__ is
defined, as with GNU C, use that; that way we don't pollute the
namespace with <stddef.h>'s symbols. Otherwise, include <stddef.h>
and use ptrdiff_t. */
#ifdef __PTRDIFF_TYPE__
# define PTR_INT_TYPE __PTRDIFF_TYPE__
#else
# include <stddef.h>
# define PTR_INT_TYPE ptrdiff_t
#endif
/* If B is the base of an object addressed by P, return the result of
aligning P to the next multiple of A + 1. B and P must be of type
char *. A + 1 must be a power of 2. */
#define __BPTR_ALIGN(B, P, A) ((B) + (((P) - (B) + (A)) & ~(A)))
/* Similar to _BPTR_ALIGN (B, P, A), except optimize the common case
where pointers can be converted to integers, aligned as integers,
and converted back again. If PTR_INT_TYPE is narrower than a
pointer (e.g., the AS/400), play it safe and compute the alignment
relative to B. Otherwise, use the faster strategy of computing the
alignment relative to 0. */
#define __PTR_ALIGN(B, P, A) \
(sizeof (PTR_INT_TYPE) < sizeof(void *) ? \
__BPTR_ALIGN((B), (P), (A)) : \
(void *)__BPTR_ALIGN((PTR_INT_TYPE)(void *)0, (PTR_INT_TYPE)(P), (A)) \
)
#include <string.h>
struct _obstack_chunk /* Lives at front of each chunk. */
{
char *limit; /* 1 past end of this chunk */
struct _obstack_chunk *prev; /* address of prior chunk or NULL */
char contents[4]; /* objects begin here */
};
struct obstack /* control current object in current chunk */
{
long chunk_size; /* preferred size to allocate chunks in */
struct _obstack_chunk *chunk; /* address of current struct obstack_chunk */
char *object_base; /* address of object we are building */
char *next_free; /* where to add next char to current object */
char *chunk_limit; /* address of char after current chunk */
union
{
PTR_INT_TYPE tempint;
void *tempptr;
} temp; /* Temporary for some macros. */
int alignment_mask; /* Mask of alignment for each object. */
/* These prototypes vary based on `use_extra_arg'. */
union {
void *(*plain) (long);
struct _obstack_chunk *(*extra) (void *, long);
} chunkfun;
union {
void (*plain) (void *);
void (*extra) (void *, struct _obstack_chunk *);
} freefun;
void *extra_arg; /* first arg for chunk alloc/dealloc funcs */
unsigned use_extra_arg:1; /* chunk alloc/dealloc funcs take extra arg */
unsigned maybe_empty_object:1;/* There is a possibility that the current
chunk contains a zero-length object. This
prevents freeing the chunk if we allocate
a bigger chunk to replace it. */
unsigned alloc_failed:1; /* No longer used, as we now call the failed
handler on error, but retained for binary
compatibility. */
};
/* Declare the external functions we use; they are in obstack.c. */
extern void _obstack_newchunk (struct obstack *, int);
extern int _obstack_begin (struct obstack *, int, int,
void *(*) (long), void (*) (void *));
extern int _obstack_begin_1 (struct obstack *, int, int,
void *(*) (void *, long),
void (*) (void *, void *), void *);
extern int _obstack_memory_used (struct obstack *);
void obstack_free (struct obstack *, void *);
/* Error handler called when `obstack_chunk_alloc' failed to allocate
more memory. This can be set to a user defined function which
should either abort gracefully or use longjump - but shouldn't
return. The default action is to print a message and abort. */
extern void (*obstack_alloc_failed_handler) (void);
/* Pointer to beginning of object being allocated or to be allocated next.
Note that this might not be the final address of the object
because a new chunk might be needed to hold the final size. */
#define obstack_base(h) ((void *) (h)->object_base)
/* Size for allocating ordinary chunks. */
#define obstack_chunk_size(h) ((h)->chunk_size)
/* Pointer to next byte not yet allocated in current chunk. */
#define obstack_next_free(h) ((h)->next_free)
/* Mask specifying low bits that should be clear in address of an object. */
#define obstack_alignment_mask(h) ((h)->alignment_mask)
/* To prevent prototype warnings provide complete argument list. */
#define obstack_init(h) \
_obstack_begin ((h), 0, 0, \
(void *(*) (long)) obstack_chunk_alloc, \
(void (*) (void *)) obstack_chunk_free)
#define obstack_begin(h, size) \
_obstack_begin ((h), (size), 0, \
(void *(*) (long)) obstack_chunk_alloc, \
(void (*) (void *)) obstack_chunk_free)
#define obstack_specify_allocation(h, size, alignment, chunkfun, freefun) \
_obstack_begin ((h), (size), (alignment), \
(void *(*) (long)) (chunkfun), \
(void (*) (void *)) (freefun))
#define obstack_specify_allocation_with_arg(h, size, alignment, chunkfun, freefun, arg) \
_obstack_begin_1 ((h), (size), (alignment), \
(void *(*) (void *, long)) (chunkfun), \
(void (*) (void *, void *)) (freefun), (arg))
#define obstack_chunkfun(h, newchunkfun) \
((h)->chunkfun.extra = (struct _obstack_chunk *(*)(void *, long)) (newchunkfun))
#define obstack_freefun(h, newfreefun) \
((h)->freefun.extra = (void (*)(void *, struct _obstack_chunk *)) (newfreefun))
#define obstack_1grow_fast(h,achar) (*((h)->next_free)++ = (achar))
#define obstack_blank_fast(h,n) ((h)->next_free += (n))
#define obstack_memory_used(h) _obstack_memory_used (h)
#if defined __GNUC__ && defined __STDC__ && __STDC__
/* NextStep 2.0 cc is really gcc 1.93 but it defines __GNUC__ = 2 and
does not implement __extension__. But that compiler doesn't define
__GNUC_MINOR__. */
# if __GNUC__ < 2 || (__NeXT__ && !__GNUC_MINOR__)
# define __extension__
# endif
/* For GNU C, if not -traditional,
we can define these macros to compute all args only once
without using a global variable.
Also, we can avoid using the `temp' slot, to make faster code. */
# define obstack_object_size(OBSTACK) \
__extension__ \
({ struct obstack const *__o = (OBSTACK); \
(unsigned) (__o->next_free - __o->object_base); })
# define obstack_room(OBSTACK) \
__extension__ \
({ struct obstack const *__o = (OBSTACK); \
(unsigned) (__o->chunk_limit - __o->next_free); })
# define obstack_make_room(OBSTACK,length) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
int __len = (length); \
if (__o->chunk_limit - __o->next_free < __len) \
_obstack_newchunk (__o, __len); \
(void) 0; })
# define obstack_empty_p(OBSTACK) \
__extension__ \
({ struct obstack const *__o = (OBSTACK); \
(__o->chunk->prev == 0 \
&& __o->next_free == __PTR_ALIGN ((char *) __o->chunk, \
__o->chunk->contents, \
__o->alignment_mask)); })
# define obstack_grow(OBSTACK,where,length) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
int __len = (length); \
if (__o->next_free + __len > __o->chunk_limit) \
_obstack_newchunk (__o, __len); \
memcpy (__o->next_free, where, __len); \
__o->next_free += __len; \
(void) 0; })
# define obstack_grow0(OBSTACK,where,length) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
int __len = (length); \
if (__o->next_free + __len + 1 > __o->chunk_limit) \
_obstack_newchunk (__o, __len + 1); \
memcpy (__o->next_free, where, __len); \
__o->next_free += __len; \
*(__o->next_free)++ = 0; \
(void) 0; })
# define obstack_1grow(OBSTACK,datum) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + 1 > __o->chunk_limit) \
_obstack_newchunk (__o, 1); \
obstack_1grow_fast (__o, datum); \
(void) 0; })
/* These assume that the obstack alignment is good enough for pointers
or ints, and that the data added so far to the current object
shares that much alignment. */
# define obstack_ptr_grow(OBSTACK,datum) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + sizeof (void *) > __o->chunk_limit) \
_obstack_newchunk (__o, sizeof (void *)); \
obstack_ptr_grow_fast (__o, datum); }) \
# define obstack_int_grow(OBSTACK,datum) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + sizeof (int) > __o->chunk_limit) \
_obstack_newchunk (__o, sizeof (int)); \
obstack_int_grow_fast (__o, datum); })
# define obstack_ptr_grow_fast(OBSTACK,aptr) \
__extension__ \
({ struct obstack *__o1 = (OBSTACK); \
*(const void **) __o1->next_free = (aptr); \
__o1->next_free += sizeof (const void *); \
(void) 0; })
# define obstack_int_grow_fast(OBSTACK,aint) \
__extension__ \
({ struct obstack *__o1 = (OBSTACK); \
*(int *) __o1->next_free = (aint); \
__o1->next_free += sizeof (int); \
(void) 0; })
# define obstack_blank(OBSTACK,length) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
int __len = (length); \
if (__o->chunk_limit - __o->next_free < __len) \
_obstack_newchunk (__o, __len); \
obstack_blank_fast (__o, __len); \
(void) 0; })
# define obstack_alloc(OBSTACK,length) \
__extension__ \
({ struct obstack *__h = (OBSTACK); \
obstack_blank (__h, (length)); \
obstack_finish (__h); })
# define obstack_copy(OBSTACK,where,length) \
__extension__ \
({ struct obstack *__h = (OBSTACK); \
obstack_grow (__h, (where), (length)); \
obstack_finish (__h); })
# define obstack_copy0(OBSTACK,where,length) \
__extension__ \
({ struct obstack *__h = (OBSTACK); \
obstack_grow0 (__h, (where), (length)); \
obstack_finish (__h); })
/* The local variable is named __o1 to avoid a name conflict
when obstack_blank is called. */
# define obstack_finish(OBSTACK) \
__extension__ \
({ struct obstack *__o1 = (OBSTACK); \
void *__value = (void *) __o1->object_base; \
if (__o1->next_free == __value) \
__o1->maybe_empty_object = 1; \
__o1->next_free \
= __PTR_ALIGN (__o1->object_base, __o1->next_free, \
__o1->alignment_mask); \
if (__o1->next_free - (char *)__o1->chunk \
> __o1->chunk_limit - (char *)__o1->chunk) \
__o1->next_free = __o1->chunk_limit; \
__o1->object_base = __o1->next_free; \
__value; })
# define obstack_free(OBSTACK, OBJ) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
void *__obj = (OBJ); \
if (__obj > (void *)__o->chunk && __obj < (void *)__o->chunk_limit) \
__o->next_free = __o->object_base = (char *)__obj; \
else (obstack_free) (__o, __obj); })
#else /* not __GNUC__ or not __STDC__ */
# define obstack_object_size(h) \
(unsigned) ((h)->next_free - (h)->object_base)
# define obstack_room(h) \
(unsigned) ((h)->chunk_limit - (h)->next_free)
# define obstack_empty_p(h) \
((h)->chunk->prev == 0 \
&& (h)->next_free == __PTR_ALIGN ((char *) (h)->chunk, \
(h)->chunk->contents, \
(h)->alignment_mask))
/* Note that the call to _obstack_newchunk is enclosed in (..., 0)
so that we can avoid having void expressions
in the arms of the conditional expression.
Casting the third operand to void was tried before,
but some compilers won't accept it. */
# define obstack_make_room(h,length) \
( (h)->temp.tempint = (length), \
(((h)->next_free + (h)->temp.tempint > (h)->chunk_limit) \
? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0))
# define obstack_grow(h,where,length) \
( (h)->temp.tempint = (length), \
(((h)->next_free + (h)->temp.tempint > (h)->chunk_limit) \
? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0), \
memcpy ((h)->next_free, where, (h)->temp.tempint), \
(h)->next_free += (h)->temp.tempint)
# define obstack_grow0(h,where,length) \
( (h)->temp.tempint = (length), \
(((h)->next_free + (h)->temp.tempint + 1 > (h)->chunk_limit) \
? (_obstack_newchunk ((h), (h)->temp.tempint + 1), 0) : 0), \
memcpy ((h)->next_free, where, (h)->temp.tempint), \
(h)->next_free += (h)->temp.tempint, \
*((h)->next_free)++ = 0)
# define obstack_1grow(h,datum) \
( (((h)->next_free + 1 > (h)->chunk_limit) \
? (_obstack_newchunk ((h), 1), 0) : 0), \
obstack_1grow_fast (h, datum))
# define obstack_ptr_grow(h,datum) \
( (((h)->next_free + sizeof (char *) > (h)->chunk_limit) \
? (_obstack_newchunk ((h), sizeof (char *)), 0) : 0), \
obstack_ptr_grow_fast (h, datum))
# define obstack_int_grow(h,datum) \
( (((h)->next_free + sizeof (int) > (h)->chunk_limit) \
? (_obstack_newchunk ((h), sizeof (int)), 0) : 0), \
obstack_int_grow_fast (h, datum))
# define obstack_ptr_grow_fast(h,aptr) \
(((const void **) ((h)->next_free += sizeof (void *)))[-1] = (aptr))
# define obstack_int_grow_fast(h,aint) \
(((int *) ((h)->next_free += sizeof (int)))[-1] = (aint))
# define obstack_blank(h,length) \
( (h)->temp.tempint = (length), \
(((h)->chunk_limit - (h)->next_free < (h)->temp.tempint) \
? (_obstack_newchunk ((h), (h)->temp.tempint), 0) : 0), \
obstack_blank_fast (h, (h)->temp.tempint))
# define obstack_alloc(h,length) \
(obstack_blank ((h), (length)), obstack_finish ((h)))
# define obstack_copy(h,where,length) \
(obstack_grow ((h), (where), (length)), obstack_finish ((h)))
# define obstack_copy0(h,where,length) \
(obstack_grow0 ((h), (where), (length)), obstack_finish ((h)))
# define obstack_finish(h) \
( ((h)->next_free == (h)->object_base \
? (((h)->maybe_empty_object = 1), 0) \
: 0), \
(h)->temp.tempptr = (h)->object_base, \
(h)->next_free \
= __PTR_ALIGN ((h)->object_base, (h)->next_free, \
(h)->alignment_mask), \
(((h)->next_free - (char *) (h)->chunk \
> (h)->chunk_limit - (char *) (h)->chunk) \
? ((h)->next_free = (h)->chunk_limit) : 0), \
(h)->object_base = (h)->next_free, \
(h)->temp.tempptr)
# define obstack_free(h,obj) \
( (h)->temp.tempint = (char *) (obj) - (char *) (h)->chunk, \
((((h)->temp.tempint > 0 \
&& (h)->temp.tempint < (h)->chunk_limit - (char *) (h)->chunk)) \
? (ptrdiff_t) ((h)->next_free = (h)->object_base \
= (h)->temp.tempint + (char *) (h)->chunk) \
: (((obstack_free) ((h), (h)->temp.tempint + (char *) (h)->chunk), 0), 0)))
#endif /* not __GNUC__ or not __STDC__ */
#ifdef __cplusplus
} /* C++ */
#endif
#endif /* obstack.h */
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