Based on glibc 2.33 -> 2.34, there is one new feature:

NEWS for version 2.34 ===================== Major new features: * Add _SC_MINSIGSTKSZ and _SC_SIGSTKSZ. When _DYNAMIC_STACK_SIZE_SOURCE or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are no longer constant on Linux. MINSIGSTKSZ is redefined to sysconf(_SC_MINSIGSTKSZ) and SIGSTKSZ is redefined to sysconf (_SC_SIGSTKSZ). This supports dynamic sized register sets for modern architectural features like Arm SVE. =====================

If _SC_SIGSTKSZ_SOURCE or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are redefined as:

/* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ). */ # undef SIGSTKSZ # define SIGSTKSZ sysconf (_SC_SIGSTKSZ)

/* Minimum stack size for a signal handler: SIGSTKSZ. */ # undef MINSIGSTKSZ # define MINSIGSTKSZ SIGSTKSZ

Compilation will fail if the source assumes constant MINSIGSTKSZ or SIGSTKSZ.

Build error with the GNU C Library 2.34: DEBUG: | sigreturn.c:150:13: error: variably modified 'altstack_data' at file scope | sigreturn.c:150:13: error: variably modified 'altstack_data' at file scope DEBUG: | 150 | static char altstack_data[SIGSTKSZ]; | 150 | static char altstack_data[SIGSTKSZ]; DEBUG: | | ^~~~~~~~~~~~~

DEBUG: | single_step_syscall.c:60:22: error: variably modified 'altstack_data' at file scope DEBUG: | 60 | static unsigned char altstack_data[SIGSTKSZ]; DEBUG: | | ^~~~~~~~~~~~~

Link: https://sourceware.org/pipermail/libc-alpha/2021-January/121996.html Link: https://sourceware.org/pipermail/libc-alpha/2021-August/129718.html Suggested-by: Jianwei Hu jianwei.hu@windriver.com Signed-off-by: Jun Miao jun.miao@windriver.com --- tools/testing/selftests/x86/mov_ss_trap.c | 4 ++-- tools/testing/selftests/x86/sigreturn.c | 7 +++---- tools/testing/selftests/x86/single_step_syscall.c | 4 ++-- tools/testing/selftests/x86/syscall_arg_fault.c | 7 +++---- 4 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/x86/mov_ss_trap.c b/tools/testing/selftests/x86/mov_ss_trap.c index 6da0ac3f0135..cc3de6ff9fba 100644 --- a/tools/testing/selftests/x86/mov_ss_trap.c +++ b/tools/testing/selftests/x86/mov_ss_trap.c @@ -47,7 +47,6 @@ unsigned short ss; extern unsigned char breakpoint_insn[]; sigjmp_buf jmpbuf; -static unsigned char altstack_data[SIGSTKSZ];

static void enable_watchpoint(void) { @@ -250,13 +249,14 @@ int main() if (sigsetjmp(jmpbuf, 1) == 0) { printf("[RUN]\tMOV SS; SYSENTER\n"); stack_t stack = { - .ss_sp = altstack_data, + .ss_sp = malloc(sizeof(char) * SIGSTKSZ), .ss_size = SIGSTKSZ, }; if (sigaltstack(&stack, NULL) != 0) err(1, "sigaltstack"); sethandler(SIGSEGV, handle_and_longjmp, SA_RESETHAND | SA_ONSTACK); nr = SYS_getpid; + free(stack.ss_sp); /* Clear EBP first to make sure we segfault cleanly. */ asm volatile ("xorl %%ebp, %%ebp; mov %[ss], %%ss; SYSENTER" : "+a" (nr) : [ss] "m" (ss) : "flags", "rcx" diff --git a/tools/testing/selftests/x86/sigreturn.c b/tools/testing/selftests/x86/sigreturn.c index 57c4f67f16ef..5d7961a5f7f6 100644 --- a/tools/testing/selftests/x86/sigreturn.c +++ b/tools/testing/selftests/x86/sigreturn.c @@ -138,9 +138,6 @@ static unsigned short LDT3(int idx) return (idx << 3) | 7; }

-/* Our sigaltstack scratch space. */ -static char altstack_data[SIGSTKSZ]; - static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), int flags) { @@ -771,7 +768,8 @@ int main() setup_ldt();

stack_t stack = { - .ss_sp = altstack_data, + /* Our sigaltstack scratch space. */ + .ss_sp = malloc(sizeof(char) * SIGSTKSZ), .ss_size = SIGSTKSZ, }; if (sigaltstack(&stack, NULL) != 0) @@ -872,5 +870,6 @@ int main() total_nerrs += test_nonstrict_ss(); #endif

+ free(stack.ss_sp); return total_nerrs ? 1 : 0; } diff --git a/tools/testing/selftests/x86/single_step_syscall.c b/tools/testing/selftests/x86/single_step_syscall.c index 120ac741fe44..9a30f443e928 100644 --- a/tools/testing/selftests/x86/single_step_syscall.c +++ b/tools/testing/selftests/x86/single_step_syscall.c @@ -57,7 +57,6 @@ static void clearhandler(int sig)

static volatile sig_atomic_t sig_traps, sig_eflags; sigjmp_buf jmpbuf; -static unsigned char altstack_data[SIGSTKSZ];

#ifdef __x86_64__ # define REG_IP REG_RIP @@ -210,7 +209,7 @@ int main() unsigned long nr = SYS_getpid; printf("[RUN]\tSet TF and check SYSENTER\n"); stack_t stack = { - .ss_sp = altstack_data, + .ss_sp = malloc(sizeof(char) * SIGSTKSZ), .ss_size = SIGSTKSZ, }; if (sigaltstack(&stack, NULL) != 0) @@ -219,6 +218,7 @@ int main() SA_RESETHAND | SA_ONSTACK); sethandler(SIGILL, print_and_longjmp, SA_RESETHAND); set_eflags(get_eflags() | X86_EFLAGS_TF); + free(stack.ss_sp); /* Clear EBP first to make sure we segfault cleanly. */ asm volatile ("xorl %%ebp, %%ebp; SYSENTER" : "+a" (nr) :: "flags", "rcx" #ifdef __x86_64__ diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c b/tools/testing/selftests/x86/syscall_arg_fault.c index bff474b5efc6..461fa41a4d02 100644 --- a/tools/testing/selftests/x86/syscall_arg_fault.c +++ b/tools/testing/selftests/x86/syscall_arg_fault.c @@ -17,9 +17,6 @@

#include "helpers.h"

-/* Our sigaltstack scratch space. */ -static unsigned char altstack_data[SIGSTKSZ]; - static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), int flags) { @@ -104,7 +101,8 @@ static void sigill(int sig, siginfo_t *info, void *ctx_void) int main() { stack_t stack = { - .ss_sp = altstack_data, + /* Our sigaltstack scratch space. */ + .ss_sp = malloc(sizeof(char) * SIGSTKSZ), .ss_size = SIGSTKSZ, }; if (sigaltstack(&stack, NULL) != 0) @@ -233,5 +231,6 @@ int main() set_eflags(get_eflags() & ~X86_EFLAGS_TF); #endif

+ free(stack.ss_sp); return 0; }