https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103525
Bug ID: 103525
Summary: [RISCV] wrong function entry with
-fpatchable-function-entry
Product: gcc
Version: 10.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: demangler
Assignee: unassigned at gcc dot gnu.org
Reporter: wcohen at redhat dot com
Target Milestone: ---
Created attachment 51914
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51914&action=edit
Reproducer to show DW_AT_low_pc doesn't always match label for function entry.
When the riscv linux kernel was compiled with CONFIG_DYNAMIC_FTRACE=y the
addresses listed in DW_AT_low_pc in the debuginfo and the /proc/kallsyms did
not match. The difference was 0x10 bytes. The /proc/kallsyms entry would
point to the function label and the DW_AT_low_pc in the DIE for the function
would point to the first instruction after the 8 nop instructions created by
the -fpatchable-function-entry=8 enable by the CONFIG_DYNAMIC_FTRACE=y. This
seems to be similar to pr99217 for mips.
Can demonstrate the problem with gcc-10.3.1 with the small reproducer
u32_test.c:
$ rpm -q gcc
gcc-10.3.1-1.fc33.riscv64
$ gcc -fpatchable-function-entry=8 -g -O2 -save-temps u32_test.c -o u32_test
$ llvm-dwarfdump --name="main" u32_test
u32_test: file format elf64-littleriscv
0x000000cf: DW_TAG_subprogram
DW_AT_external (true)
DW_AT_name ("main")
DW_AT_decl_file ("/home/riscv/u32_test.c")
DW_AT_decl_line (8)
DW_AT_decl_column (0x01)
DW_AT_prototyped (true)
DW_AT_type (0x00000030 "int")
DW_AT_low_pc (0x00000000000103f0)
DW_AT_high_pc (0x000000000001040a)
DW_AT_frame_base (DW_OP_call_frame_cfa)
DW_AT_GNU_all_call_sites (true)
DW_AT_sibling (0x0000013c)
$ nm u32_test |grep main
U __libc_start_main@@GLIBC_2.27
00000000000103e0 T main
$gcc -g -O2 -save-temps u32_test.c -o u32_test
$ llvm-dwarfdump --name="main" u32_test
u32_test: file format elf64-littleriscv
0x000000cf: DW_TAG_subprogram
DW_AT_external (true)
DW_AT_name ("main")
DW_AT_decl_file ("/home/riscv/u32_test.c")
DW_AT_decl_line (8)
DW_AT_decl_column (0x01)
DW_AT_prototyped (true)
DW_AT_type (0x00000030 "int")
DW_AT_low_pc (0x00000000000103e0)
DW_AT_high_pc (0x00000000000103fa)
DW_AT_frame_base (DW_OP_call_frame_cfa)
DW_AT_GNU_all_call_sites (true)
DW_AT_sibling (0x0000013c)
$ nm u32_test |grep main
U __libc_start_main@@GLIBC_2.27
00000000000103e0 T main
