> To be clear, the error I'm seeing with the example is this: > > /usr/libexec/gcc/arm-3ds-none-eabi/ld: warning: cannot find entry symbol _start; defaulting to 0000000000008018 > /usr/libexec/gcc/arm-3ds-none-eabi/ld: /tmp/ccPp7lyA.ltrans0.ltrans.o: in function `f': > /home/gabriel/tmp/t1.c:3: undefined reference to `malloc' > collect2: error: ld returned 1 exit status > > > I would start by adding -Wl,-y,malloc to last gcc command line (the link step > with '-o main') to see how linker sees references to malloc. You can do that > both with and without -flto to compare successful/failing scenarios. > > If you have both BFD and Gold linker, try both (-fuse-ld=gold or =bfd). > > You can also pass -Wl,-v to see the linker command line and compare it with > non-LTO compilation (or even native compilation). > > Does it work if you pass -fno-builtin-malloc to compilation of t.c? > > It looks like without the option, GCC LTO plugin does not see malloc as an > undefined symbol in t.o, the linker does not unpack malloc from libc, and when > LTO plugin passes a new object file that references malloc, it's too late. > > I believe linkers had some hacks to help this case (rescanning libc for new > references from LTO object files), but I'm not exactly sure, it's been a while > since I looked at a related area. > > Alexander So, on a native x86_64 build -Wm,-y,malloc returns: /usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /lib64/libc.so.6: definition of malloc /usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: /tmp/ccJJ05Rd.ltrans0.ltrans.o: reference to malloc With the arm cross compiler: /usr/libexec/gcc/arm-none-eabi/ld: /tmp/ccupVhtJ.ltrans0.ltrans.o: reference to malloc /usr/libexec/gcc/arm-none-eabi/ld: /tmp/ccupVhtJ.ltrans0.ltrans.o: in function `f': /home/gabriel/tmp/t1.c:3: undefined reference to `malloc' collect2: error: ld returned 1 exit status So it's just not finding the symbol? With gold it looks like it's having problems loading the LTO plugin: /tmp/ccUp7UC6.ltrans0.ltrans.o: reference to malloc /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/libg.a(lib_a-malloc.o): plugin needed to handle lto object /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/libg.a(lib_a-malloc.o): plugin needed to handle lto object /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/libc.a(lib_a-malloc.o): plugin needed to handle lto object /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/libc.a(lib_a-malloc.o): plugin needed to handle lto object /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/crt0.o(.text+0x11c): error: undefined reference to '__bss_start__' /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/crt0.o(.text+0x120): error: undefined reference to '__bss_end__' t1.c:3: error: undefined reference to 'malloc' collect2: error: ld returned 1 exit status But I see the plugin specified in the ld.gold invocation with -Wl,-v as -plugin /usr/libexec/gcc/arm-none-eabi/11.1.0/liblto_plugin.so There are also some additional plugin-opts being passed on. The gold linker works fine on the native x86_64 build. I'm not seeing anything glaringly different between the ld invocation for the native build and arm. I'll try to format the arm ld output: /usr/libexec/gcc/arm-none-eabi/ld -plugin /usr/libexec/gcc/arm-none-eabi/11.1.0/liblto_plugin.so -plugin-opt=/usr/libexec/gcc/arm-none-eabi/11.1.0/lto-wrapper -plugin-opt=-fresolution=/tmp/ccxcs2NR.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lg -plugin-opt=-pass-through=-lc --sysroot=/usr/arm-none-eabi -X -o main /usr/lib/gcc/arm-none-eabi/11.1.0/crti.o /usr/lib/gcc/arm-none-eabi/11.1.0/crtbegin.o /usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib/crt0.o -L/usr/lib/gcc/arm-none-eabi/11.1.0 -L/usr/lib/gcc/arm-none-eabi/11.1.0/../../../../arm-none-eabi/lib -L/usr/arm-none-eabi/lib -L/usr/arm-none-eabi/usr/lib -y malloc -v main.o t1.o --start-group -lgcc -lg -lc --end-group /usr/lib/gcc/arm-none-eabi/11.1.0/crtend.o /usr/lib/gcc/arm-none-eabi/11.1.0/crtn.o And... yeah, with -fno-builtin-malloc, it appears to build! So, it looks like a bug in the linker? Although, I'm somewhat surprised gold is also having issues. Gabe Marcano
