[ This report is based on fedora patch gdb-glibc-strstr-workaround.patch (see also PR glibc/14166). ] Consider a hello world a.out with debug info. Without glibc debug info installed, I'm able to call strstr: ... $ gdb -q a.out -ex start -ex "p strstr" -ex "ptype strstr" Reading symbols from a.out... Temporary breakpoint 1 at 0x40051b: file hello.c, line 6. Starting program: /data/vries/gdb/a.out Temporary breakpoint 1, main () at hello.c:6 6 printf ("hello\n"); $1 = {<text gnu-indirect-function variable, no debug info>} 0x7ffff7e4f9ce <strstr> type = <unknown return type> () (gdb) p strstr ("haha", "ah") '__strstr_sse2_unaligned' has unknown return type; cast the call to its declared return type (gdb) p (char *)strstr ("haha", "ah") $2 = 0x7ffff7dab1b1 "aha" (gdb) ... Now with glibc debug info installed: ... $ gdb -q a.out -ex start -ex "p strstr" -ex "ptype strstr" Reading symbols from a.out... Temporary breakpoint 1 at 0x40051b: file hello.c, line 6. Starting program: /data/vries/gdb/a.out Temporary breakpoint 1, main () at hello.c:6 6 printf ("hello\n"); $1 = {<text gnu-indirect-function variable, no debug info>} 0x7ffff7e4e9ce <__libc_strstr_ifunc> type = <unknown return type> () (gdb) p strstr ("haha", "ah") $2 = void (gdb) p (char *)strstr ("haha", "ah") Invalid cast. (gdb) ... This is with glibc 2.31 on openSUSE Leap 15.4. With glibc 2.38 on openSUSE Tumbleweed this doesn't happen. This seems to be caused by the fact that in the tumbleweed case we have an unspecified_type return type: ... <1><11dd5e>: Abbrev Number: 1 (DW_TAG_subprogram) <11dd5f> DW_AT_name : __strstr_sse2_unaligned <11dd63> DW_AT_external : 1 <11dd63> DW_AT_type : <0x11dd6e> <11dd64> DW_AT_low_pc : 0xb9c9e <11dd6c> DW_AT_high_pc : 1173 <1><11dd6e>: Abbrev Number: 3 (DW_TAG_unspecified_type) <1><11dd6f>: Abbrev Number: 0 ... and in the failing case there's no type at all, which defaults to void: ... <1><3e1e58>: Abbrev Number: 2 (DW_TAG_subprogram) <3e1e59> DW_AT_name : __strstr_sse2_unaligned <3e1e5d> DW_AT_external : 1 <3e1e5e> DW_AT_low_pc : 0xbbd2e <3e1e66> DW_AT_high_pc : 0xbc1c3 ... This is basically PR gas/29517, fixed in 2.40 but present in 2.39. What is curious though is that we do manage to find the correct type for the revolver function: ... (gdb) p __libc_strstr_ifunc $3 = {char *(*(void))(const char *, const char *)} 0x7ffff7e4e9ce <__libc_strstr_ifunc> ... but we don't use it.
Tentative fix: swap the order here: ... diff --git a/gdb/infcall.c b/gdb/infcall.c index 0f9ad34bbb4..20d0f9acca5 100644 --- a/gdb/infcall.c +++ b/gdb/infcall.c @@ -316,17 +316,20 @@ find_function_addr (struct value *function, FUNCTION_TYPE have been asked for. */ if (retval_type != NULL || function_type != NULL) { - type *target_ftype = find_function_type (funaddr); - /* If we don't have debug info for the target function, - see if we can instead extract the target function's - type from the type that the resolver returns. */ - if (target_ftype == NULL) - target_ftype = find_gnu_ifunc_target_type (resolver_addr); + /* Try to get the target function's type from the type that + the resolver returns. We do this first to work around + PR gas/29517. */ + type *target_ftype = find_gnu_ifunc_target_type (resolver_addr); if (target_ftype != NULL) { value_type = check_typedef (target_ftype)->target_type (); ftype = target_ftype; } + + /* Try to get the target function's type from the target + function. */ + if (target_ftype == NULL) + target_ftype = find_function_type (funaddr); } } else ...
(In reply to Tom de Vries from comment #1) > Tentative fix: swap the order here: And we get: ... FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=0: final_debug=1: p gnu_ifunc (3) FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=0: resolver_debug=0: final_debug=1: p gnu_ifunc() FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=0: final_debug=1: p gnu_ifunc (3) FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=0: final_debug=1: p gnu_ifunc() ...
Alternatively, we detect the problem while reading the debug info and fix it: ... diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 5bbc8e24cf9..e547653d7fe 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -10161,7 +10161,20 @@ read_func_scope (struct die_info *die, struct dwarf2_cu *cu) gdb_assert (cu->get_builder () != nullptr); newobj = cu->get_builder ()->push_context (0, lowpc); - newobj->name = new_symbol (die, read_type_die (die, cu), cu, templ_func); + struct type *type = read_type_die (die, cu); + if (type->code () == TYPE_CODE_FUNC + && type->num_fields () == 0 + && type->target_type ()->code () == TYPE_CODE_VOID + && !type->target_type ()->is_stub () + && strcmp (cu->producer, "GNU AS 2.39.0") == 0) + { + /* Work around PR gas/29517. */ + type = (type_allocator (cu->per_objfile->objfile, cu->lang ()) + .new_type (TYPE_CODE_VOID, 0, nullptr)); + type->set_is_stub (true); + set_die_type (die, type, cu); + } + newobj->name = new_symbol (die, type, cu, templ_func); if (dwarf2_func_is_main_p (die, cu)) set_objfile_main_name (objfile, newobj->name->linkage_name (), ...
https://sourceware.org/pipermail/gdb-patches/2023-September/202828.html
The master branch has been updated by Tom de Vries <vries@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1d45d90934b10862c00a22bcf4075815a785001b commit 1d45d90934b10862c00a22bcf4075815a785001b Author: Tom de Vries <tdevries@suse.de> Date: Mon Oct 16 16:32:28 2023 +0200 [gdb/symtab] Work around PR gas/29517 When using glibc debuginfo generated with gas 2.39, we run into PR gas/29517: ... $ gdb -q -batch a.out -ex start -ex "p (char *)strstr (\"haha\", \"ah\")" Temporary breakpoint 1 at 0x40051b: file hello.c, line 6. Temporary breakpoint 1, main () at hello.c:6 6 printf ("hello\n"); Invalid cast. ... while without glibc debuginfo installed we get the expected result: ... $n = 0x7ffff7daa1b1 "aha" ... and likewise with glibc debuginfo generated with gas 2.40. The strstr ifunc resolves to __strstr_sse2_unaligned. The problem is that gas generates dwarf that states that the return type is void: ... <1><3e1e58>: Abbrev Number: 2 (DW_TAG_subprogram) <3e1e59> DW_AT_name : __strstr_sse2_unaligned <3e1e5d> DW_AT_external : 1 <3e1e5e> DW_AT_low_pc : 0xbbd2e <3e1e66> DW_AT_high_pc : 0xbc1c3 ... while the return type should be a DW_TAG_unspecified_type, as is the case with gas 2.40. We can still use the workaround of casting to another function type for both __strstr_sse2_unaligned: ... (gdb) p ((char * (*) (const char *, const char *))__strstr_sse2_unaligned) \ ("haha", "ah") $n = 0x7ffff7daa211 "aha" ... and strstr (which requires using *strstr to dereference the ifunc before we cast): ... gdb) p ((char * (*) (const char *, const char *))*strstr) ("haha", "ah") $n = 0x7ffff7daa251 "aha" ... but that's a bit cumbersome to use. Work around this in the dwarf reader, such that we have instead: ... (gdb) p (char *)strstr ("haha", "ah") $n = 0x7ffff7daa1b1 "aha" ... This also requires fixing producer_is_gcc to stop returning true for producer "GNU AS 2.39.0". Tested on x86_64-linux. Approved-By: Andrew Burgess <aburgess@redhat.com> PR symtab/30911 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30911
Fixed.