RISC-V: Clarify the addends of pc-relative access.
The original discussion was here,
https://github.com/riscv/riscv-elf-psabi-doc/issues/184
After discussing with Kito Cheng, I think the addends of %pcrel_hi
and %pcrel_lo are both allowed in GNU toolchain. However, both of
the them mean the offset of symbols, rather than the pc address.
But the addends of %got_pcrel_hi and it's %pcrel_lo do not look
reasonable. I believe gcc won't generate the got patterns with
addends, so linker should report dangerous relocation errors,
in case the assembly code use them.
Another issue was here,
https://sourceware.org/pipermail/binutils/2021-June/116983.html
At the beginnig, I suppose %pcrel_hi and %pcrel_lo are valid only
when they are in the same input section. But Jim Wilson points out
that gcc may generate %hi and %lo in the different input sections,
when -freorder-blocks-and-partition option is used. So that a memory
references for a loop may have the %hi outside the loop, but the %lo
remain in the loop. However, it is hard to create the testcases,
to see if %pcrel_hi and %pcrel_lo have the same behavior.
Unfortunately, I notice that the current pcrel resolver cannot
work for the above case. For now we build a hash table for pcrel
at the start of riscv_elf_relocate_section, and then free the hash
at the end. But riscv_elf_relocate_section only handles an input
section at a time, so that means we can only resolve the %pcrel_hi
and %pcrel_lo which are in the same input section. Otherwise, like
the above case, we will report "%pcrel_lo missing matching %pcrel_hi"
for them. I have no plan to improve this in the short-term, so maybe
we can wait until someone meets the problem before we deal with it.
bfd/
* elfnn-riscv.c (riscv_pcrel_hi_reloc): Added field to store
the original relocation type, in case the type is converted to
R_RISCV_HI20.
(riscv_pcrel_lo_reloc): Removed unused name field.
(riscv_pcrel_relocs): Added comments.
(riscv_zero_pcrel_hi_reloc): Removed unused input_bfd.
(riscv_record_pcrel_hi_reloc): Updated.
(riscv_record_pcrel_lo_reloc): Likewise.
(riscv_resolve_pcrel_lo_relocs): Likewise. Check the original
type of auipc, to make sure the %pcrel_lo without any addends.
Otherwise, report dangerous relocation error.
(riscv_elf_relocate_section): Updated above functions are changed.
For R_RISCV_GOT_HI20, report dangerous relocation error when addend
isn't zero.
ld/
* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3a.d: New testcase.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3a.s: Likewise.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3b.d: New testcase.
Should report error since the %pcrel_lo with addend refers to
%got_pcrel_hi.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3b.s: Likewise.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3c.d: New testcase.
Should report error since the %got_pcrel_hi with addend.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3c.s: Likewise.
* testsuite/ld-riscv-elf/pcrel-lo-addend-3.ld: Likewise.
2021-06-22 12:02:52 +08:00
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#source: pcrel-lo-addend-3a.s
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#as: -march=rv64i -mabi=lp64 -mno-relax
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#ld: -m[riscv_choose_lp64_emul] -Tpcrel-lo-addend-3.ld
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#objdump: -d
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#...
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Disassembly of section .text:
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0+900000000 <_start>:
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.*:[ ]+[0-9a-f]+[ ]+lui[ ]+a5,0x2
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.*:[ ]+[0-9a-f]+[ ]+ld[ ]+a0,0\(a5\) # 2000 <ll>
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.*:[ ]+[0-9a-f]+[ ]+ld[ ]+a0,4\(a5\)
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.*:[ ]+[0-9a-f]+[ ]+lui[ ]+a5,0x2
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.*:[ ]+[0-9a-f]+[ ]+ld[ ]+a0,4\(a5\) # 2004 <ll\+0x4>
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.*:[ ]+[0-9a-f]+[ ]+ld[ ]+a0,8\(a5\)
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.*:[ ]+[0-9a-f]+[ ]+lui[ ]+a5,0x1
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.*:[ ]+[0-9a-f]+[ ]+ld[ ]+a0,8\(a5\) # 1008 <_GLOBAL_OFFSET_TABLE_\+0x8>
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#pass
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