Wrong sign extension for 32bit relocations

[BrunoASMauricio]

The following minimal example showcases how the 32 bit relocation symbol R_ARC_32_ME is malfunctioning.

asm.S

.text
.global main
.align 4
main:

1001:
  st 1, [0xF0000008]
  j @1001b

tarc.ld

ENTRY(main)
SECTIONS
{
 . = 0x80000100;
 .text : { *(.text) }
}

Compiling it with:
arc64-elf-gcc asm.S -mcpu=hs6x --specs=nsim.specs -T tarc.ld -nostartfiles -nostdlib

Yields

/tmp/ccpBYbhK.o: in function `main':
(.text+0xc): relocation truncated to fit: R_ARC_32_ME against `no symbol'
collect2: error: ld returned 1 exit status

This happens because the 0x8000_0000 gets sign extended when it shouldn't. Replacing that value with 0x7000_0000 "fixes this".
It is expected for these values to be unsigned.

[BrunoASMauricio]

After cross-referencing the 32 bit relocations that are set as "signed" in include/elf/arc-reloc.def with the ABI, we can take two conclusions:

1. ARC_32_ME_S is NOT IN THE ABI, nor does it seem to be used anywhere (created issue Relocation symbol ARC_32_ME_S is defined but not used #565 for this)
2. There are quite a few 32 bit relocations that the ABI does not specify are signed/unsigned but are set as signed. A table of the respective entries in the ABI follows:

Enum	Hex	ELF Reloc Type	Description	Details
18	0x12	R_ARC_SDA32	SDA relocation	word32 = ME ((S+A)-SDA_BASE)
27	0x1b	R_ARC_32_ME	Runtime relocation	word32 = ME (S + A)
30	0x1e	R_ARC_SDA32_ME	SDA relocation	word32 = ME ((S+A)-SDA_BASE)
49	0x31	R_ARC_32_PCREL	PC-relative (data)	word32 = (S+A-PDATA)
50	0x32	R_ARC_PC32	PC-relative	word32 = ME (S+A-P)
51	0x33	R_ARC_GOTPC32	PC-relative GOT reference	word32 = ME (GOT + G + A - P)
52	0x34	R_ARC_PLT32	PC-relative (PLT)	word32 = ME (L+A-P)
54	0x36	R_ARC_GLOB_DAT	GOT relocation	word32= S
55	0x37	R_ARC_JMP_SLOT	Runtime relocation	word32 = ME(S)
56	0x38	R_ARC_RELATIVE	Runtime relocation	word32 = ME(B+A)
57	0x39	R_ARC_GOTOFF	GOT relocation	word32 = ME(S+A-GOT)
58	0x3a	R_ARC_GOTPC	PC-relative (GOT)	word32 = ME(GOT_BEGIN - P)
98	0x62	R_ARC_PCLO32_ME_2	PC-relative address	word32 = ME ((S + A - P ) >> 2)
99	0x63	R_ARC_PLT34	PC-relative (PLT)	word32 = ME ((L + A - P ) >> 2)

@claziss besides R_ARC_32_ME, which of these should be set to bitfield?

[claziss]

@BrunoASMauricio corrected relocs types:

Enum	Hex	ELF Reloc Type	Type	Details
18	0x12	R_ARC_SDA32	signed	word32 = ((S+A)-SDA_BASE)
27	0x1b	R_ARC_32_ME	bitfiled	word32 = ME (S + A)
30	0x1e	R_ARC_SDA32_ME	signed	word32 = ME ((S+A)-SDA_BASE)
49	0x31	R_ARC_32_PCREL	signed	word32 = (S+A-PDATA)
50	0x32	R_ARC_PC32	signed	word32 = ME (S+A-P)
51	0x33	R_ARC_GOTPC32	signed	word32 = ME (GOT + G + A - P)
52	0x34	R_ARC_PLT32	signed	word32 = ME (L+A-P)
54	0x36	R_ARC_GLOB_DAT	bitfiled	word32= S
55	0x37	R_ARC_JMP_SLOT	bitfiled	word32 = ME(S)
56	0x38	R_ARC_RELATIVE	bitfiled	word32 = ME(B+A)
57	0x39	R_ARC_GOTOFF	signed	word32 = ME(S+A-GOT)
58	0x3a	R_ARC_GOTPC	signed	word32 = ME(GOT_BEGIN - P)
98	0x62	R_ARC_PCLO32_ME_2	signed	word32 = ME ((S + A - P ) >> 2)
99	0x63	R_ARC_PLT34	signed	word32 = ME ((L + A - P ) >> 2)