[Tarantool-patches] [PATCH luajit 1/2] symtab: fix static symtab dump
Sergey Kaplun
skaplun at tarantool.org
Sat Jul 16 10:21:13 MSK 2022
Hi, Maxim!
Thanks for the patch!
LGTM, with several comments below.
On 04.07.22, Maxim Kokryashkin wrote:
> The `dl_iterate_phdr` returns an empty string as a name for
> the executable from which it was called.
Don't get: why it is the problem? I.e. why it is problem to obtain the
main symbol table? Is it sysprof parser restrictions?
> It is still possible
> to access its dynamic symbol table, but it is vital for
> sysprof to obtain the main symbol table for the LuaJIT
> executable. To do so, we need a valid path to the executable.
>
> Since there is no way to obtain the path to a running executable
> using the C standard library, this commit adds call to
> `readlink` to gather the symbolic link from `/proc/self/exe`.
> Most of the UNIX-based systems have procfs, so it is not
> a problem.
>
> Needed for tarantool/tarantool#7244
> ---
> src/lj_symtab.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/src/lj_symtab.c b/src/lj_symtab.c
> index 2b2b205b..23696401 100644
> --- a/src/lj_symtab.c
> +++ b/src/lj_symtab.c
> @@ -16,10 +16,12 @@
>
> #if LJ_HASRESOLVER
>
> +#include <linux/limits.h>
> #include <elf.h>
> #include <link.h>
> #include <stdio.h>
> #include <sys/auxv.h>
> +#include <unistd.h>
> #include "lj_gc.h"
> #endif
>
> @@ -352,6 +354,7 @@ static int resolve_symbolnames(struct dl_phdr_info *info, size_t info_size,
> struct lj_wbuf *buf = conf->buf;
> lua_State *L = conf->L;
> const uint8_t header = conf->header;
> + char executable_path[PATH_MAX] = "";
Why do we need this initialization? ^
>
> uint32_t lib_cnt = 0;
>
> @@ -387,6 +390,31 @@ static int resolve_symbolnames(struct dl_phdr_info *info, size_t info_size,
> ** Main way: try to open ELF and read SHT_SYMTAB, SHT_STRTAB and SHT_HASH
> ** sections from it.
> */
> +
> + /*
> + ** The `dl_iterate_phdr` returns an empty string as a name for
> + ** the executable from which it was called. It is still possible to
> + ** access its dynamic symbol table, but it is vital for sysprof to obtain
> + ** the main symbol table for the LuaJIT executable. To do so, we need a
> + ** valid path to the executable. Since there is no way to obtain the
> + ** path to a running executable using the C standard library, the only
> + ** more or less reliable way to do this is by reading the symbolic link
> + ** from `/proc/self/exe`. Most of the UNIX-based systems have procfs, so
> + ** it is not a problem.
> + */
> + if (*info->dlpi_name == 0) {
Nit: s/0/'\0'/ to emphasize that we check that string contains only NULL
char.
> + if (-1 != readlink("/proc/self/exe", executable_path, PATH_MAX))
Nit: `readlink("/proc/self/exe", executable_path, PATH_MAX) != -1`
> + info->dlpi_name = executable_path;
> + else
> + /*
> + ** It is impossible for sysprof to function properly without the
> + ** LuaJIT's .symtab section present. The assertion below
> + ** is unlikely to be triggered on any system supported by sysprof,
> + ** unless someone have deleted the LuaJIT binary right after the
> + ** start.
> + */
> + lua_assert(0);
> + }
> if (dump_sht_symtab(info->dlpi_name, buf, L, header, info->dlpi_addr) == 0) {
> ++conf->cur_lib;
> }
> --
> 2.36.1
>
--
Best regards,
Sergey Kaplun
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