debug_info missing parameters for naked functions

[c1ed623a-df99-497b-81ca-bca6dae737a4]

Bugzilla Link	38824
Version	trunk
OS	Linux
Attachments	source file
CC	@adrian-prantl,@dwblaikie,@JDevlieghere,@pogo59,@rnk

Extended Description

Source file:

extern "C" void naked_function(int value, char name); extern "C" void regular_function(int value, char name);

void attribute((naked, noinline)) naked_function(int value, char* name) { }

void regular_function(int value, char* name) { }

Command line: clang++ -g --shared -fPIC -o libtest.so src.cc

Result: $ readelf -wi libtest.so Contents of the .debug_info section:

Compilation Unit @ offset 0x0: Length: 0x81 (32-bit) Version: 4 Abbrev Offset: 0x0 Pointer Size: 8

<0>: Abbrev Number: 1 (DW_TAG_compile_unit) DW_AT_producer : (indirect string, offset: 0x0): clang version 8.0.0 (https://git.llvm.org/git/clang.git/ 1bc73590ad1335313e8f262393547b8af67c9167) (https://git.llvm.org/git/llvm.git/ 24a8df2c420ee959f27acae6bac2969cdd0a5388) <10> DW_AT_language : 4 (C++) <12> DW_AT_name : (indirect string, offset: 0xb1): src.cc <16> DW_AT_stmt_list : 0x0 <1a> DW_AT_comp_dir : (indirect string, offset: 0xb8): /ssd/llvm/test/naked_debug_info <1e> DW_AT_low_pc : 0x610 <26> DW_AT_high_pc : 0x1d <1><2a>: Abbrev Number: 2 (DW_TAG_subprogram) <2b> DW_AT_low_pc : 0x610 <33> DW_AT_high_pc : 0x7 <37> DW_AT_frame_base : 1 byte block: 56 (DW_OP_reg6 (rbp)) <39> DW_AT_name : (indirect string, offset: 0xd8): naked_function <3d> DW_AT_decl_file : 1 <3e> DW_AT_decl_line : 4 <3f> DW_AT_external : 1 <1><3f>: Abbrev Number: 3 (DW_TAG_subprogram) <40> DW_AT_low_pc : 0x620 <48> DW_AT_high_pc : 0xd <4c> DW_AT_frame_base : 1 byte block: 56 (DW_OP_reg6 (rbp)) <4e> DW_AT_name : (indirect string, offset: 0xe7): regular_function <52> DW_AT_decl_file : 1 <53> DW_AT_decl_line : 7 <54> DW_AT_external : 1 <2><54>: Abbrev Number: 4 (DW_TAG_formal_parameter) <55> DW_AT_location : 2 byte block: 91 7c (DW_OP_fbreg: -4) <58> DW_AT_name : (indirect string, offset: 0xf8): value <5c> DW_AT_decl_file : 1 <5d> DW_AT_decl_line : 7 <5e> DW_AT_type : <0x71> <2><62>: Abbrev Number: 4 (DW_TAG_formal_parameter) <63> DW_AT_location : 2 byte block: 91 70 (DW_OP_fbreg: -16) <66> DW_AT_name : (indirect string, offset: 0x102): name <6a> DW_AT_decl_file : 1 <6b> DW_AT_decl_line : 7 <6c> DW_AT_type : <0x78> <2><70>: Abbrev Number: 0 <1><71>: Abbrev Number: 5 (DW_TAG_base_type) <72> DW_AT_name : (indirect string, offset: 0xfe): int <76> DW_AT_encoding : 5 (signed) <77> DW_AT_byte_size : 4 <1><78>: Abbrev Number: 6 (DW_TAG_pointer_type) <79> DW_AT_type : <0x7d> <1><7d>: Abbrev Number: 5 (DW_TAG_base_type) <7e> DW_AT_name : (indirect string, offset: 0x107): char <82> DW_AT_encoding : 6 (signed char) <83> DW_AT_byte_size : 1 <1><84>: Abbrev Number: 0 Note that while parameters for not naked function are preserved naked function parameters are lost.

[dwblaikie]

What Reid said sounds about right.

Another thing we could do/check is that the parameter DILocalVariables end up in the "retainedNodes" list associated with the DISubprogram. So the function type is correct even if no locations are identified inside the function.

[rnk]

We emit debug info for parameters during CodeGenFunction::EmitFunctionProlog, and marking a function naked prevents prologue emission, as expected.

To fix it, we'd need to emit llvm.dbg.value intrinsics instead of llvm.dbg.declare intrinsics, since all we have are SSA registers to talk about, no allocas. We'd need to call DIBuilder::insertDbgValueIntrinsic.