It came up on a rust bug (https://github.com/rust-lang/rust/issues/41252) that gdb producer-sniffs for "clang" (e.g. in i386-tdep.c). A simple fix would be to allow "rustc" as well here. There doesn't seem to be a generic way to sniff for "LLVM back end". However, I wonder whether it makes sense now to switch to a producer blacklist rather than a whitelist.
I'm testing a patch for this, that changes gdb to use a blacklist instead. I'm not sure if this will be acceptable, since the initial blacklist is empty.
Maybe this was wishful thinking since there are some regressions if I switch to an empty blacklist. I'm still looking into whether maybe there are just certain old versions of gcc (4.x perhaps) that were bad here. Otherwise, I have a different patch that just adds rustc to the check.
One specific regression is gdb.ada/ref_param.exp, which fails because gdb starts believing the DWARF line table. But I think the line table is correct and the test might be wrong. CU: /home/tromey/gdb/binutils-gdb/gdb/testsuite/gdb.ada/ref_param/pck.adb: File name Line number Starting address pck.adb 18 0x4012be pck.adb 18 0x4012be pck.adb 20 0x4012c6 pck.adb 21 0x4012d7 pck.adb 23 0x4012e5 With my current patch, the breakpoint is set on line 18. Without it, it is set at line 20. Doesn't line 18 seem correct though?
In commit 154f2735ad4 ("[gdb/testsuite] Fix gdb.ada/access_tagged_param.exp for aarch64") I did: ... -if ![runto call_me] then { +if ![runto pck.adb:20] then { ... to make the test-case robust against problems in prologue analysis. Of course problems in prologue analysis need to be fixed, but we don't want to be exposed to this in lots of unrelated test-cases, which then fail on some but not on other architectures, hence the fix. Anyway, let's change this back, and look at what's generated: ... (gdb) break call_me^M Breakpoint 1 at 0x401f9a: file /home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb, line 20.^M ... So, it looks like gdb decided that the first 3 insns are prologue: ... 0000000000401f92 <pck__call_me>: 401f92: 55 push %rbp 401f93: 48 89 e5 mov %rsp,%rbp 401f96: 48 89 7d f8 mov %rdi,-0x8(%rbp) 401f9a: 48 8b 45 f8 mov -0x8(%rbp),%rax ... Using additional_flags=-fdump-rtl-all and looking at pck.adb.309r.final we can confirm that the first 2 insns are prologue: ... (note 4 1 32 2 [bb 2] NOTE_INSN_BASIC_BLOCK) (insn/f 32 4 33 2 (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0 S8 A8]) (reg/f:DI 6 bp)) "/home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb":18 57 {*pushdi2_rex64} (nil)) (insn/f 33 32 34 2 (set (reg/f:DI 6 bp) (reg/f:DI 7 sp)) "/home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb":18 81 {*movdi_internal} (nil)) (insn 34 33 35 2 (set (mem/v:BLK (scratch:DI) [0 A8]) (unspec:BLK [ (mem/v:BLK (scratch:DI) [0 A8]) ] UNSPEC_MEMORY_BLOCKAGE)) "/home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb":18 687 {*memory_blockage} (nil)) (note 35 34 2 2 NOTE_INSN_PROLOGUE_END) (insn 2 35 3 2 (set (mem/f/c:DI (plus:DI (reg/f:DI 6 bp) (const_int -8 [0xfffffffffffffff8])) [5 d+0 S8 A64]) (reg:DI 5 di [ d ])) "/home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb":18 81 {*movdi_internal} (nil)) (note 3 2 6 2 NOTE_INSN_FUNCTION_BEG) ... and the third insn is in the twilight zone between prologue end and function begin, and depending on your definition of prologue, can be still considered part of the prologue. Note that due to compiling at -O0, there's no .debug_loc contribution, so the DW_AT_location expression for the function parameter 'D' is consider only valid after the prologue, and in this sense the third insn is certainly part of the prologue: ... (gdb) si pck.call_me (d=...) at pck.adb:18 18 procedure Call_Me (D : in out Data) is (gdb) p d $1 = (null) (gdb) si 0x0000000000401f93 18 procedure Call_Me (D : in out Data) is (gdb) p d $2 = (null) (gdb) si 0x0000000000401f96 18 procedure Call_Me (D : in out Data) is (gdb) p d $3 = (null) (gdb) si 20 if D.One > D.Two then (gdb) p d $4 = (one => 1, two => 2, three => 3, four => 4, five => 5, six => 6) (gdb) ... So, say we start to trust the dwarf line table (to be in a certain format that allows us to determine where the prologue ends). Let's do that using "maint set skip-prologue line" (https://sourceware.org/pipermail/gdb-patches/2022-August/191343.html): ... clean_restart gdb_test_no_output "maint set skip-prologue line" gdb_load ${binfile} ... Now we have the incorrect: ... (gdb) break call_me^M Breakpoint 1 at 0x401f92: file /home/vries/gdb_versions/devel/binutils-gdb.git/gdb/testsuite/gdb.ada/ref_param/pck.adb, line 18.^M ... The line table as decoded by readelf is: ... File name Line number Starting address View Stmt pck.adb 18 0x401f92 x pck.adb 18 0x401f92 1 x pck.adb 20 0x401f9a x pck.adb 21 0x401fab x pck.adb 23 0x401fb9 x pck.adb - 0x401fbd ... and the summary of that by gdb is: ... INDEX LINE ADDRESS IS-STMT PROLOGUE-END 0 18 0x0000000000401f92 Y 1 18 0x0000000000401f92 Y 2 20 0x0000000000401f9a Y 3 21 0x0000000000401fab Y 4 23 0x0000000000401fb9 Y 5 END 0x0000000000401fbd Y ... This is with gcc 7.5.0. With gcc 12.2.1, I get a line table without the entry at index 1, and things do work as expected. My hunch at this point is that this is due to gcc commit c029fcb5680 ("Reset force_source_line in final.c"), which is first present in release 11.1.0.
(In reply to Tom Tromey from comment #3) > One specific regression is gdb.ada/ref_param.exp, which fails because > gdb starts believing the DWARF line table. But I think the line table > is correct and the test might be wrong. > > CU: /home/tromey/gdb/binutils-gdb/gdb/testsuite/gdb.ada/ref_param/pck.adb: > File name Line number Starting address > pck.adb 18 0x4012be > > pck.adb 18 0x4012be > > pck.adb 20 0x4012c6 > pck.adb 21 0x4012d7 > pck.adb 23 0x4012e5 > > > With my current patch, the breakpoint is set on line 18. > Without it, it is set at line 20. > > Doesn't line 18 seem correct though? From the analysis in the previous comment, I'd say that line 20 is correct, and line 18 is incorrect. That is, the line table is incorrect due to a gcc bug.
(In reply to Tom de Vries from comment #4) > My hunch at this point is that this is due to gcc commit c029fcb5680 ("Reset > force_source_line in final.c"), which is first present in release 11.1.0. Confirmed, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108615 .