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arm64-gen.c: Better explanation of relocation choice.

master
Edmund Grimley Evans 2015-03-01 11:31:10 +00:00
parent fc119f9840
commit 883fd365c7
1 changed files with 24 additions and 21 deletions
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45
arm64-gen.c
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@ -400,27 +400,30 @@ static void gen_fstore(int sz, int dst, int bas, uint64_t off)
static void gen_addr(int r, Sym *sym, unsigned long addend)
{
#if 0
// This is normally the right way to do it, I think,
// but it does not work with "-run" when stdin or stderr is
// used by the program: "R_AARCH64_ADR_PREL_PG_HI21 relocation failed".
greloca(cur_text_section, sym, ind, R_AARCH64_ADR_PREL_PG_HI21, addend);
o(0x90000000 | r);
greloca(cur_text_section, sym, ind, R_AARCH64_ADD_ABS_LO12_NC, addend);
o(0x91000000 | r | r << 5);
#else
// This seems to work in all cases, unless you try to use an old buggy
// GCC for linking, which says: "unresolvable R_AARCH64_MOVW_UABS_G0_NC
// relocation against symbol `stderr@@GLIBC_2.17'".
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G0_NC, addend);
o(0xf2800000 | r); // movk x(rt),#...,lsl #0
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G1_NC, addend);
o(0xf2a00000 | r); // movk x(rt),#...,lsl #16
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G2_NC, addend);
o(0xf2c00000 | r); // movk x(rt),#...,lsl #32
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G3, addend);
o(0xf2e00000 | r); // movk x(rt),#...,lsl #48
#endif
// Currently TCC's linker does not generate COPY relocations for
// STT_OBJECTs when tcc is invoked with "-run". This typically
// results in "R_AARCH64_ADR_PREL_PG_HI21 relocation failed" when
// a program refers to stdin. A workaround is to avoid that
// relocation and use only relocations with unlimited range.
int avoid_adrp = 1;
if (avoid_adrp || (sym->type.t & VT_WEAK)) {
// (GCC uses a R_AARCH64_ABS64 in this case.)
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G0_NC, addend);
o(0xd2800000 | r); // mov x(rt),#0,lsl #0
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G1_NC, addend);
o(0xf2a00000 | r); // movk x(rt),#0,lsl #16
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G2_NC, addend);
o(0xf2c00000 | r); // movk x(rt),#0,lsl #32
greloca(cur_text_section, sym, ind, R_AARCH64_MOVW_UABS_G3, addend);
o(0xf2e00000 | r); // movk x(rt),#0,lsl #48
}
else {
greloca(cur_text_section, sym, ind, R_AARCH64_ADR_PREL_PG_HI21, addend);
o(0x90000000 | r);
greloca(cur_text_section, sym, ind, R_AARCH64_ADD_ABS_LO12_NC, addend);
o(0x91000000 | r | r << 5);
}
}
ST_FUNC void load(int r, SValue *sv)