Hi Serhei,
On Tue, Mar 24, 2026 at 6:38 PM Serhei Makarov <[email protected]> wrote:
>
> Since we plan to replace stacktrace with stackprof (& the associated
> test case) in a subsequent patchset, this is a minimal patch to
> illustrate where the existing code using libdwfl_stacktrace needs to
> generalize.
>
> * src/stacktrace.c: Enable for ARM architectures.
> (expected_frame_nregs): New function.
> (sp_reg_index): New function.
> (sysprof_find_dwfl): Replace hardcoded SP index with new functions.
> (sysprof_unwind_frame_cb): Likewise.
> (main): Open default_ebl backend appropriate to the current arch.
> ---
> src/stacktrace.c | 51 +++++++++++++++++++++++++++++++++++-------------
> 1 file changed, 37 insertions(+), 14 deletions(-)
>
> diff --git a/src/stacktrace.c b/src/stacktrace.c
> index 0740a2bc..c1888b67 100644
> --- a/src/stacktrace.c
> +++ b/src/stacktrace.c
> @@ -80,13 +80,14 @@
> #include <locale.h>
>
> #include <system.h>
> +#include <sys/utsname.h>
>
> #include <linux/perf_event.h>
>
> -/* TODO: Need to generalize the code beyond x86 architectures. */
> +/* TODO: Need to generalize the code beyond x86/ARM architectures. */
> #include <asm/perf_regs.h>
> -#ifndef _ASM_X86_PERF_REGS_H
> -#error "eu-stacktrace is currently limited to x86 architectures"
> +#if !defined(_ASM_X86_PERF_REGS_H) && !defined(_ASM_ARM_PERF_REGS_H) &&
> !defined(_ASM_ARM64_PERF_REGS_H)
> +#error "eu-stacktrace is currently limited to x86/ARM architectures"
configure.ac needs to be updated to check for
_ASM_ARM[64]_PERF_REGS_H. Currently --enable-stacktrace will fail on
arm/aarch64.
> #endif
>
> /*************************************
> @@ -853,6 +854,26 @@ sysprof_init_dwfl_cb (Dwflst_Process_Tracker *cb_tracker,
> return dwfl;
> }
>
> +uint32_t expected_frame_nregs (Ebl *ebl)
> +{
> + int m = ebl_get_elfmachine(ebl);
> + /* For aarch64, we use fewer and ebl->frame_nregs to unwind. */
> + if (m == EM_ARM)
Here and elsewhere in this patch there should be hanlding for EM_AARCH64 too.
> + return 14;
> + if (m == EM_X86_64 || m == EM_386)
> + return ebl_frame_nregs(ebl);
> + /* In general, it's better to be on the permissive side. */
> + return 1;
> +}
> +
> +int sp_reg_index (Ebl *ebl, bool is_abi32)
> +{
> + int m = ebl_get_elfmachine(ebl);
> + if (m == EM_X86_64 || m == EM_386) return is_abi32 ? 4 : 7;
> + else if (m == EM_ARM) return is_abi32 ? 13 : 31;
> + else return 0; /* XXX unwinding will likely not continue */
> +}
> +
> Dwfl *
> sysprof_find_dwfl (struct sysprof_unwind_info *sui,
> SysprofCaptureStackUser *ev,
> @@ -860,10 +881,7 @@ sysprof_find_dwfl (struct sysprof_unwind_info *sui,
> Elf **out_elf)
> {
> pid_t pid = ev->frame.pid;
> - /* XXX: Note that sysprof requesting the x86_64 register file from
> - perf_events will result in an array of 17 regs even for 32-bit
> - applications. */
> - if (regs->n_regs < ebl_frame_nregs(default_ebl)) /* XXX expecting
> everything except FLAGS */
> + if (regs->n_regs < expected_frame_nregs(default_ebl))
> {
> if (show_failures)
> fprintf(stderr, N_("sysprof_find_dwfl: n_regs=%d, expected %ld\n"),
> @@ -891,12 +909,11 @@ sysprof_find_dwfl (struct sysprof_unwind_info *sui,
> }
>
> reuse:
> - /* TODO: Generalize to other architectures than x86_64. */
> - sui->last_sp = regs->regs[7];
> + bool is_abi32 = (regs->abi == PERF_SAMPLE_REGS_ABI_32);
> + sui->last_sp = regs->regs[sp_reg_index(default_ebl, is_abi32)];
> sui->last_base = sui->last_sp;
>
> if (show_frames) {
> - bool is_abi32 = (regs->abi == PERF_SAMPLE_REGS_ABI_32);
> fprintf(stderr, "sysprof_find_dwfl pid %lld%s: size=%ld%s pc=%lx
> sp=%lx+(%lx)\n",
> (long long) pid, cached ? " (cached)" : "",
> ev->size, is_abi32 ? " (32-bit)" : "",
> @@ -924,11 +941,9 @@ sysprof_unwind_frame_cb (Dwfl_Frame *state, void *arg)
>
> Dwarf_Addr pc_adjusted = pc - (isactivation ? 0 : 1);
> Dwarf_Addr sp;
> - /* TODO: Need to generalize this code beyond x86 architectures. */
> struct sysprof_unwind_info *sui = (struct sysprof_unwind_info *)arg;
> int is_abi32 = (sui->last_abi == PERF_SAMPLE_REGS_ABI_32);
> - /* DWARF register order cf. elfutils backends/{x86_64,i386}_initreg.c: */
> - int user_regs_sp = is_abi32 ? 4 : 7;
> + int user_regs_sp = sp_reg_index(default_ebl, is_abi32);
> int rc = dwfl_frame_reg (state, user_regs_sp, &sp);
> if (rc < 0)
> {
> @@ -1376,7 +1391,15 @@
> https://sourceware.org/cgit/elfutils/tree/README.eu-stacktrace?h=users/serhei/eu
> error (EXIT_BAD, errno, N_("Could not initialize Dwfl table"));
>
> /* TODO: Generalize to other architectures. */
> - default_ebl = ebl_openbackend_machine(EM_X86_64);
> + struct utsname u;
> + uname(&u);
> + int em = EM_NONE;
> + if (strcmp(u.machine, "x86_64") == 0) em = EM_X86_64;
> + else if (strcmp(u.machine, "i686") == 0 || strcmp(u.machine, "i386")
> == 0) em = EM_386;
> + else if (strcmp(u.machine, "aarch64") == 0 || strcmp(u.machine,
> "armv7l")) em = EM_ARM;
strcmp(u.machine, "armv7l") is missing == 0. Also "aarch64" should set
em = EM_AARCH64 instead of EM_ARM.
Aaron
> + else
> + error (EXIT_BAD, errno, N_("Unsupported architecture: %s"),
> u.machine);
> + default_ebl = ebl_openbackend_machine(em);
>
> struct sysprof_unwind_info sui;
> sui.output_fd = output_fd;
> --
> 2.53.0
>
