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Re: armv5 userland broken

Great work!

On 29/06/2021 08:13, Rin Okuyama wrote:

I've examined assembler codes for userland libraries for arm:
common/lib/libc, csu, libc, compiler_rt, and libm, and found that
some routines in compiler_rt do not align sp correctly:


Also, some routines in libc do not also in Thumb-mode userland:


I think it's better / less ugly to push even numbers of registers rather
than adjusting sp (especially for thumb)

By fixing these, armv5 system works just fine, except for new
regression in tests/lib/libc/tls/t_tls_dlopen; the alignment fault
occurs in the above mentioned ldrd in ld.elf_so!

This seems a bug in GCC itself, since testf() in the test attempts to
call EABI runtime routines before sp is aligned:

t_tls_dlopen:     file format elf32-littlearm


00010ca0 <testf>:
   10ca0:       e92d40f0        push    {r4, r5, r6, r7, lr}
   10ca4:       ebffff4e        bl      109e4 <__aeabi_read_tp@plt>
   10ca8:       e59f41d0        ldr     r4, [pc, #464]  ; 10e80
   10cac:       e24dd00c        sub     sp, sp, #12

This seems a GCC bug for armv5 and prior, that needs function call to
obtain TLS pointer. armv6 and later use coprocessor instruction to
get TLS pointer; coprocessor instruction can be always safely used
before sp is adjusted.

It seems that there are problem in load_tp_soft{,_fdpic} in arm.md in
GCC, but I've never found how to fix it yet...



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