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[PowerPC] libc backwards compatibility shim for auxv change

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As part of the FreeBSD powerpc* flag day (1300070), the auxv numbering was
changed to match every other platform.

See D20799 for more details on that change.

While the kernel and rtld were adapted, libc was not, so old dynamic
binaries broke for reasons other than the ABI change on powerpc64.

Since it's possible to support nearly everything regarding old binaries by
adding compatibility code to libc (as besides rtld, it is the main point
where auxv is digested), we might as well provide compatibility code.

The only unhandled case remaining should be "new format libraries that call
elf_aux_info() which are dynamically linked to by old-format binaries",
which should be quite rare.

Reviewed by:	jhibbits
Sponsored by:	Tag1 Consulting, Inc.
Differential Revision:	https://reviews.freebsd.org/D23096
This commit is contained in:
Brandon Bergren 2020-01-22 02:06:34 +00:00
parent a9e3baa562
commit 0a90eb9f2f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=356966
1 changed files with 102 additions and 0 deletions
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102
lib/libc/gen/auxv.c
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@ -73,6 +73,12 @@ static char *canary, *pagesizes, *execpath;
static void *timekeep;
static u_long hwcap, hwcap2;
#ifdef __powerpc__
static int powerpc_new_auxv_format = 0;
static void _init_aux_powerpc_fixup(void);
int _powerpc_elf_aux_info(int, void *, int);
#endif
static void
init_aux(void)
{
@ -125,11 +131,107 @@ init_aux(void)
case AT_TIMEKEEP:
timekeep = aux->a_un.a_ptr;
break;
#ifdef __powerpc__
/*
* Since AT_STACKPROT is always set, and the common
* value 23 is mutually exclusive with the legacy powerpc
* value 21, the existence of AT_STACKPROT proves we are
* on the common format.
*/
case AT_STACKPROT: /* 23 */
powerpc_new_auxv_format = 1;
break;
#endif
}
}
#ifdef __powerpc__
if (!powerpc_new_auxv_format)
_init_aux_powerpc_fixup();
#endif
}
#ifdef __powerpc__
static void
_init_aux_powerpc_fixup(void)
{
Elf_Auxinfo *aux;
/*
* Before 1300070, PowerPC platforms had nonstandard numbering for
* the aux vector. When running old binaries, the kernel will pass
* the vector using the old numbering. Reload affected variables.
*/
for (aux = __elf_aux_vector; aux->a_type != AT_NULL; aux++) {
switch (aux->a_type) {
case AT_OLD_CANARY:
canary = (char *)(aux->a_un.a_ptr);
break;
case AT_OLD_CANARYLEN:
canary_len = aux->a_un.a_val;
break;
case AT_OLD_EXECPATH:
execpath = (char *)(aux->a_un.a_ptr);
break;
case AT_OLD_PAGESIZES:
pagesizes = (char *)(aux->a_un.a_ptr);
break;
case AT_OLD_PAGESIZESLEN:
pagesizes_len = aux->a_un.a_val;
break;
case AT_OLD_OSRELDATE:
osreldate = aux->a_un.a_val;
break;
case AT_OLD_NCPUS:
ncpus = aux->a_un.a_val;
break;
}
}
}
int
_powerpc_elf_aux_info(int aux, void *buf, int buflen)
{
/*
* If we are in the old auxv format, we need to translate the aux
* parameter of elf_aux_info() calls into the common auxv format.
* Internal libc calls always use the common format, and they
* directly call _elf_aux_info instead of using the weak symbol.
*/
if (!powerpc_new_auxv_format) {
switch (aux) {
case AT_OLD_EXECPATH:
aux = AT_EXECPATH;
break;
case AT_OLD_CANARY:
aux = AT_CANARY;
break;
case AT_OLD_CANARYLEN:
aux = AT_CANARYLEN;
break;
case AT_OLD_OSRELDATE:
aux = AT_OSRELDATE;
break;
case AT_OLD_NCPUS:
aux = AT_NCPUS;
break;
case AT_OLD_PAGESIZES:
aux = AT_PAGESIZES;
break;
case AT_OLD_PAGESIZESLEN:
aux = AT_PAGESIZESLEN;
break;
case AT_OLD_STACKPROT:
aux = AT_STACKPROT;
break;
}
}
return _elf_aux_info(aux, buf, buflen);
}
__weak_reference(_powerpc_elf_aux_info, elf_aux_info);
#else
__weak_reference(_elf_aux_info, elf_aux_info);
#endif
int
_elf_aux_info(int aux, void *buf, int buflen)