https://bugs.llvm.org/show_bug.cgi?id=35659
Bug ID: 35659
Summary: Change in COMMON symbol layout after "ELF: Remove
DefinedCommon."
Product: lld
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: ELF
Assignee: unassignedb...@nondot.org
Reporter: alberto.ma...@microsoft.com
CC: aaron.sm...@microsoft.com, llvm-bugs@lists.llvm.org,
pe...@pcc.me.uk
Created attachment 19548
--> https://bugs.llvm.org/attachment.cgi?id=19548&action=edit
Map files to show the different layout
LLD commit dc49c0 (https://reviews.llvm.org/D39666) causes the layout of COMMON
symbols to change in a busybox binary.
You can see this from the two map files attached (generated for x86_64):
busybox_unstripped.map.7ca03 (the common symbols are at the end of the .bss
section) generated with 7ca03, the commit before dc49c0.
busybox_unstripped.map.dc49c0 (the common symbols are at the start of the .bss
section)
(the binaries used by the linker have not changed between the two versions)
dc49c0 appears to me as an internal refactoring to LLD. Is the different layout
expected ?
I am asking because this change is causing a kernel panic when booting linux
with busybox.
For completeness at the bottom you find the command line used by the busybox
build system to link the executable (called busybox_unstripped)
(We use musl-clang as a compiler wrapper, which internally calls clang to
statically link against musl libc.a)
Notice the use of –sort-common, which might explain the difference.
If you would like to have a reproducer I can come up with one (it probably
won't be pretty though)
Many thanks in advance
Alberto
musl-clang -Wall -Wshadow -Wwrite-strings -Wundef -Wstrict-prototypes -Wunused
-Wunused-parameter -Wunused-function -Wunused-value -Wmissing-prototypes
-Wmissing-declarations -Wno-format-security -Wdeclaration-after-statement
-Wold-style-definition -fno-builtin-strlen -finline-limit=0
-fomit-frame-pointer -ffunction-sections -fdata-sections -funsigned-char
-static-libgcc -falign-functions=1 -falign-jumps=1 -falign-labels=1
-falign-loops=1 -fno-unwind-tables -fno-asynchronous-unwind-tables
-fno-builtin-printf -Os -o busybox_unstripped -Wl,--sort-common
-Wl,--sort-section,alignment -Wl,--gc-sections -Wl,--start-group
applets/built-in.o archival/lib.a archival/libarchive/lib.a console-tools/lib.a
coreutils/lib.a coreutils/libcoreutils/lib.a debianutils/lib.a e2fsprogs/lib.a
editors/lib.a findutils/lib.a init/lib.a libbb/lib.a libpwdgrp/lib.a
loginutils/lib.a mailutils/lib.a miscutils/lib.a modutils/lib.a
networking/lib.a networking/libiproute/lib.a networking/udhcp/lib.a
printutils/lib.a procps/lib.a runit/lib.a selinux/lib.a shell/lib.a
sysklogd/lib.a util-linux/lib.a util-linux/volume_id/lib.a archival/built-in.o
archival/libarchive/built-in.o console-tools/built-in.o coreutils/built-in.o
coreutils/libcoreutils/built-in.o debianutils/built-in.o e2fsprogs/built-in.o
editors/built-in.o findutils/built-in.o init/built-in.o libbb/built-in.o
libpwdgrp/built-in.o loginutils/built-in.o mailutils/built-in.o
miscutils/built-in.o modutils/built-in.o networking/built-in.o
networking/libiproute/built-in.o networking/udhcp/built-in.o
printutils/built-in.o procps/built-in.o runit/built-in.o selinux/built-in.o
shell/built-in.o sysklogd/built-in.o util-linux/built-in.o
util-linux/volume_id/built-in.o -Wl,--end-group -Wl,--start-group
-Wl,--end-group -Wl,--warn-common -Wl,-Map,busybox_unstripped.map
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