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- On ELF, ``-gz`` now defaults to ``-gz=zlib`` with the integrated assembler. - On ELF, ``-gz`` now defaults to ``-gz=zlib`` with the integrated assembler.
It produces ``SHF_COMPRESSED`` style compression of debug information. GNU It produces ``SHF_COMPRESSED`` style compression of debug information. GNU
binutils 2.26 or newer, or lld is required to link produced object files. Use binutils 2.26 or newer, or lld is required to link produced object files. Use
``-gz=zlib-gnu`` to get the old behavior. ``-gz=zlib-gnu`` to get the old behavior.
- Now that `this` pointers are tagged with `nonnull` and `dereferenceable(N)`, - Now that `this` pointers are tagged with `nonnull` and `dereferenceable(N)`,
`-fno-delete-null-pointer-checks` has gained the power to remove the `-fno-delete-null-pointer-checks` has gained the power to remove the
`nonnull` attribute on `this` for configurations that need it to be nullable. `nonnull` attribute on `this` for configurations that need it to be nullable.
- ``-gsplit-dwarf`` no longer implies ``-g2``.
thakisUnsubmitted
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This apparently bit us (chromium) in thinlto configs. Could this here be more explicit that -gsplit-dwarf now needs an explicit -g2 in cflags, and if using thinlto, in ldflags as well?

thakis: This apparently bit us (chromium) in thinlto configs. Could this here be more explicit that `…
dblaikieUnsubmitted
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Arguably I think maybe it should be fixed/made to work for (thin)lto with -g2 in cflags and -gsplit-dwarf in ldflags, without the need to specify -g2 in ldflags (if that's what you're saying is currently required). Since the -gN level would hopefully at best be ignored (because the IR carries the N in -gN with it, and it'd be unfortunate it enabling split dwarf meant you had to ignore all your per-file -gN levels, or that the -gN is ignored except for allowing -gsplit-dwarf to be respected).

@MaskRay ?

dblaikie: Arguably I think maybe it should be fixed/made to work for (thin)lto with -g2 in cflags and…
MaskRayAuthorUnsubmitted
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LLD LTO does not have debug related options. ld -g is an ignored compatibility option. LLD somewhat inherited that from GNU ld. I don't think -gsplit-dwarf or -g can be separately controlled in ldflags.

@thakis Can you share the crbug.com discussion thread?

MaskRay: LLD LTO does not have debug related options. `ld -g` is an ignored compatibility option. LLD…
dblaikieUnsubmitted
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Hmm, I guess the thing that bit Chromium would've been the need to add -g2 to cflags where previously it might've been just -gsplit-dwarf for cflags and ldflags.

But it doesn't look like -g2 is needed in ldflags, only passing it to the compilation seems sufficient, then the -gsplit-dwarf passed to the link step is respected:

$ clang++-tot -flto=thin test.cpp -g -c && clang++-tot -flto=thin -fuse-ld=lld -gsplit-dwarf test.o && llvm-dwarfdump-tot a.out
a.out:  file format elf64-x86-64

.debug_info contents:
0x00000000: Compile Unit: length = 0x0000002c, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000030)

0x0000000b: DW_TAG_compile_unit
              DW_AT_stmt_list   (0x00000000)
              DW_AT_comp_dir    ("/usr/local/google/home/blaikie/dev/scratch")
              DW_AT_GNU_dwo_name        ("a.out_dwo/1.dwo")
              DW_AT_GNU_dwo_id  (0xf29563d7c812deae)
              DW_AT_low_pc      (0x0000000000201730)
              DW_AT_high_pc     (0x0000000000201738)
              DW_AT_GNU_addr_base       (0x00000000)
$ clang++-tot -flto=thin test.cpp -g -c && clang++-tot -flto=thin -fuse-ld=lld  test.o && llvm-dwarfdump-tot a.out
a.out:  file format elf64-x86-64

.debug_info contents:
0x00000000: Compile Unit: length = 0x00000047, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x0000004b)

0x0000000b: DW_TAG_compile_unit
              DW_AT_producer    ("clang version 12.0.0 (git@github.com:llvm/llvm-project.git 0d88d7d82bc44b211a8187650a06c6cd3492186a)")
              DW_AT_language    (DW_LANG_C_plus_plus_14)
              DW_AT_name        ("test.cpp")
              DW_AT_stmt_list   (0x00000000)
              DW_AT_comp_dir    ("/usr/local/google/home/blaikie/dev/scratch")
              DW_AT_low_pc      (0x0000000000201730)
              DW_AT_high_pc     (0x0000000000201738)

0x0000002a:   DW_TAG_subprogram
                DW_AT_low_pc    (0x0000000000201730)
                DW_AT_high_pc   (0x0000000000201738)
                DW_AT_frame_base        (DW_OP_reg6 RBP)
                DW_AT_name      ("main")
                DW_AT_decl_file ("/usr/local/google/home/blaikie/dev/scratch/test.cpp")
                DW_AT_decl_line (3)
                DW_AT_type      (0x00000043 "int")
                DW_AT_external  (true)

0x00000043:   DW_TAG_base_type
                DW_AT_name      ("int")
                DW_AT_encoding  (DW_ATE_signed)
                DW_AT_byte_size (0x04)

0x0000004a:   NULL
dblaikie: Hmm, I guess the thing that bit Chromium would've been the need to add -g2 to cflags where…
New Pragmas in Clang New Pragmas in Clang
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- ... - ...
Attribute Changes in Clang Attribute Changes in Clang
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