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Add AT_BSDFLAGS auxv entry.

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The intent is to provide bsd-specific flags relevant to interpreter
and C runtime.  I did not want to reuse AT_FLAGS which is common ELF
auxv entry.

Use bsdflags to report kernel support for sigfastblock(2).  This
allows rtld and libthr to safely infer the syscall presence without
SIGSYS.  The tunable kern.elf{32,64}.sigfastblock blocks reporting.

Tested by:	pho
Disscussed with:	cem, emaste, jilles
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D12773
This commit is contained in:
Konstantin Belousov 2020-02-09 12:10:37 +00:00
parent f88c67a625
commit 944cf37bb5
3 changed files with 16 additions and 1 deletions
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7
sys/kern/imgact_elf.c
View File

@ -183,6 +183,11 @@ SYSCTL_INT(ASLR_NODE_OID, OID_AUTO, stack_gap, CTLFLAG_RW,
__XSTRING(__CONCAT(ELF, __ELF_WORD_SIZE))
": maximum percentage of main stack to waste on a random gap");
static int __elfN(sigfastblock) = 1;
SYSCTL_INT(__CONCAT(_kern_elf, __ELF_WORD_SIZE), OID_AUTO, sigfastblock,
CTLFLAG_RWTUN, &__elfN(sigfastblock), 0,
"enable sigfastblock for new processes");
static Elf_Brandinfo *elf_brand_list[MAX_BRANDS];
#define aligned(a, t) (rounddown2((u_long)(a), sizeof(t)) == (u_long)(a))
@ -1366,6 +1371,8 @@ __elfN(freebsd_copyout_auxargs)(struct image_params *imgp, uintptr_t base)
AUXARGS_ENTRY(pos, AT_HWCAP, *imgp->sysent->sv_hwcap);
if (imgp->sysent->sv_hwcap2 != NULL)
AUXARGS_ENTRY(pos, AT_HWCAP2, *imgp->sysent->sv_hwcap2);
AUXARGS_ENTRY(pos, AT_BSDFLAGS, __elfN(sigfastblock) ?
ELF_BSDF_SIGFASTBLK : 0);
AUXARGS_ENTRY(pos, AT_NULL, 0);
free(imgp->auxargs, M_TEMP);

4
sys/sys/elf_common.h
View File

@ -954,8 +954,9 @@ typedef struct {
#define AT_EHDRFLAGS 24 /* e_flags field from elf hdr */
#define AT_HWCAP 25 /* CPU feature flags. */
#define AT_HWCAP2 26 /* CPU feature flags 2. */
#define AT_BSDFLAGS 27 /* ELF BSD Flags. */
#define AT_COUNT 27 /* Count of defined aux entry types. */
#define AT_COUNT 28 /* Count of defined aux entry types. */
/*
* Relocation types.
@ -1456,5 +1457,6 @@ typedef struct {
#define R_X86_64_TLSDESC 36
#define R_X86_64_IRELATIVE 37
#define ELF_BSDF_SIGFASTBLK 0x0001 /* Kernel supports fast sigblock */
#endif /* !_SYS_ELF_COMMON_H_ */

6
usr.bin/procstat/procstat_auxv.c
View File

@ -196,6 +196,12 @@ procstat_auxv(struct procstat *procstat, struct kinfo_proc *kipp)
xo_emit("{dw:/%s}{Lw:/%-16s/%s}{:AT_HWCAP2/%#lx}\n",
prefix, "AT_HWCAP2", (u_long)auxv[i].a_un.a_val);
break;
#endif
#ifdef AT_BSDFLAGS
case AT_BSDFLAGS:
xo_emit("{dw:/%s}{Lw:/%-16s/%s}{:AT_BSDFLAGS/%#lx}\n",
prefix, "AT_BSDFLAGS", (u_long)auxv[i].a_un.a_val);
break;
#endif
default:
xo_emit("{dw:/%s}{Lw:/%16ld/%ld}{:UNKNOWN/%#lx}\n",