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[REVERTME] riscv/arch_elf.c: Handle PCREL_HI20/LO12_I/S relocations c…
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…orrectly

[REVERTME] This patch is a stripped version from upstream, there are too
many changes to the changed modules (would need to pull dozens of commits)
so only the RISC-V elf linker is updated.

There is a problem with the current elf loader for risc-v: when a pair of
PCREL_HI20 / LO12 relocations are encountered, it is assumed that these
will follow each other immediately, as follows:

label:
	auipc      a0, %pcrel_hi(symbol)    // R_RISCV_PCREL_HI20
	load/store a0, %pcrel_lo(label)(a0) // R_RISCV_PCREL_LO12_I/S

With this assumption, the hi/lo relocations are both done when a hi20
relocation entry is encountered, first to the current instruction (addr)
and to the next instruction (addr + 4).

However, this assumption is wrong. There is nothing in the elf relocation
specification[1] that mandates this. Thus, the hi/lo relocation always
needs to first fixup the hi-part, and when the lo-part is encountered, it
needs to find the corresponding hi relocation entry, via the given "label".
This necessitates (re-)visiting the relocation entries for the current
section as well as looking for "label" in the symbol table.

The NuttX elf loader does not allow such operations to be done in the
machine specific part, so this patch fixes the relocation issue by
introducing an architecture specific cache for the hi20 relocation and
symbol table entries. When a lo12 relocation is encountered, the cache
can be consulted to find the hi20 part.

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc
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@pussuw
pussuw committed Dec 13, 2023
1 parent f41bf81 commit 29c2080
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Showing 4 changed files with 189 additions and 29 deletions.
21 changes: 21 additions & 0 deletions arch/risc-v/include/elf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -83,4 +83,25 @@
#define R_RISCV_SET32 56
#define R_RISCV_32_PCREL 57

#define ARCH_ELFDATA 1
#define ARCH_ELF_RELCNT 8

/****************************************************************************
* Public Types
****************************************************************************/

#ifndef __ASSEMBLY__

struct arch_elfdata_s
{
struct hi20_rels_s
{
uintptr_t hi20_rel;
uintptr_t hi20_offset;
}
hi20_rels[ARCH_ELF_RELCNT];
};
typedef struct arch_elfdata_s arch_elfdata_t;

#endif /* __ASSEMBLY__ */
#endif /* __ARCH_RISCV_INCLUDE_ELF_H */
21 changes: 19 additions & 2 deletions binfmt/libelf/libelf_bind.c
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,15 @@
# define elf_dumpbuffer(m,b,n)
#endif

#ifdef ARCH_ELFDATA
# define ARCH_ELFDATA_DEF arch_elfdata_t arch_data; \
memset(&arch_data, 0, sizeof(arch_elfdata_t))
# define ARCH_ELFDATA_PARM &arch_data
#else
# define ARCH_ELFDATA_DEF
# define ARCH_ELFDATA_PARM NULL
#endif

/****************************************************************************
* Private Types
****************************************************************************/
Expand Down Expand Up @@ -185,6 +194,10 @@ static int elf_relocate(FAR struct elf_loadinfo_s *loadinfo, int relidx,
int i;
int j;

/* Define potential architecture specific elf data container */

ARCH_ELFDATA_DEF;

rels = kmm_malloc(CONFIG_ELF_RELOCATION_BUFFERCOUNT * sizeof(Elf_Rel));
if (rels == NULL)
{
Expand Down Expand Up @@ -334,7 +347,7 @@ static int elf_relocate(FAR struct elf_loadinfo_s *loadinfo, int relidx,

/* Now perform the architecture-specific relocation */

ret = up_relocate(rel, sym, addr);
ret = up_relocate(rel, sym, addr, ARCH_ELFDATA_PARM);
if (ret < 0)
{
berr("ERROR: Section %d reloc %d: Relocation failed: %d\n",
Expand Down Expand Up @@ -370,6 +383,10 @@ static int elf_relocateadd(FAR struct elf_loadinfo_s *loadinfo, int relidx,
int i;
int j;

/* Define potential architecture specific elf data container */

ARCH_ELFDATA_DEF;

relas = kmm_malloc(CONFIG_ELF_RELOCATION_BUFFERCOUNT * sizeof(Elf_Rela));
if (relas == NULL)
{
Expand Down Expand Up @@ -519,7 +536,7 @@ static int elf_relocateadd(FAR struct elf_loadinfo_s *loadinfo, int relidx,

/* Now perform the architecture-specific relocation */

ret = up_relocateadd(rela, sym, addr);
ret = up_relocateadd(rela, sym, addr, ARCH_ELFDATA_PARM);
if (ret < 0)
{
berr("ERROR: Section %d reloc %d: Relocation failed: %d\n",
Expand Down
6 changes: 3 additions & 3 deletions include/nuttx/elf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -142,9 +142,9 @@ bool up_checkarch(FAR const Elf_Ehdr *hdr);

#ifdef CONFIG_LIBC_ARCH_ELF
int up_relocate(FAR const Elf_Rel *rel, FAR const Elf_Sym *sym,
uintptr_t addr);
int up_relocateadd(FAR const Elf_Rela *rel,
FAR const Elf_Sym *sym, uintptr_t addr);
uintptr_t addr, FAR void *arch_data);
int up_relocateadd(FAR const Elf_Rela *rel, FAR const Elf_Sym *sym,
uintptr_t addr, FAR void *arch_data);
#endif

/****************************************************************************
Expand Down
170 changes: 146 additions & 24 deletions libs/libc/machine/risc-v/arch_elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -178,6 +178,84 @@ static void _calc_imm(long offset, long *imm_hi, long *imm_lo)
*imm_hi = hi;
}

/****************************************************************************
* Name: _add_hi20
*
* Description:
* Add PCREL_HI20 relocation offset to the LUT. When a PCREL_LO12_I/_S is
* encountered, the corresponding PCREL_HI20 value can be found from it.
*
* Input Parameters:
* arch_data - Where the PCREL_HI20 relocations are listed.
* hi20_rel - The PCREL_HI20 relocation entry.
* hi20_offset - The corresponding offset value.
*
* Returned Value:
* None.
*
****************************************************************************/

static void _add_hi20(void *arch_data, uintptr_t hi20_rel,
uintptr_t hi20_offset)
{
arch_elfdata_t *data = (arch_elfdata_t *)arch_data;
int i;

/* Try to find a free slot from the list */

for (i = 0; i < ARCH_ELF_RELCNT; i++)
{
struct hi20_rels_s *hi20 = &data->hi20_rels[i];

if (hi20->hi20_rel == 0)
{
hi20->hi20_rel = hi20_rel;
hi20->hi20_offset = hi20_offset;
break;
}
}
}

/****************************************************************************
* Name: _find_hi20
*
* Description:
* Find PCREL_HI20 relocation offset from the LUT. When a PCREL_LO12_I/_S
* is encountered, the corresponding PCREL_HI20 value is needed to do the
* relocation.
*
* Input Parameters:
* arch_data - Where the PCREL_HI20 relocations are listed.
* hi20_rel - The PCREL_HI20 relocation entry.
*
* Returned Value:
* The corresponding hi20_offset value.
*
****************************************************************************/

static uintptr_t _find_hi20(void *arch_data, uintptr_t hi20_rel)
{
arch_elfdata_t *data = (arch_elfdata_t *)arch_data;
int i;

/* Try to find the hi20 value from the list */

for (i = 0; i < ARCH_ELF_RELCNT; i++)
{
struct hi20_rels_s *hi20 = &data->hi20_rels[i];

if (hi20->hi20_rel == hi20_rel)
{
/* Found it, we can clear the entry now */

hi20->hi20_rel = 0;
return hi20->hi20_offset;
}
}

return 0;
}

/****************************************************************************
* Public Functions
****************************************************************************/
Expand Down Expand Up @@ -266,14 +344,15 @@ bool up_checkarch(const Elf_Ehdr *ehdr)
*
****************************************************************************/

int up_relocate(const Elf_Rel *rel, const Elf_Sym *sym, uintptr_t addr)
int up_relocate(const Elf_Rel *rel, const Elf_Sym *sym, uintptr_t addr,
void *arch_data)
{
berr("Not implemented\n");
return -ENOSYS;
}

int up_relocateadd(const Elf_Rela *rel, const Elf_Sym *sym,
uintptr_t addr)
uintptr_t addr, void *arch_data)
{
long offset;
unsigned int relotype;
Expand Down Expand Up @@ -317,58 +396,101 @@ int up_relocateadd(const Elf_Rela *rel, const Elf_Sym *sym,
break;

case R_RISCV_PCREL_LO12_I:
case R_RISCV_PCREL_LO12_S:
{
long imm_hi;
long imm_lo;

binfo("%s at %08" PRIxPTR " [%08" PRIx32 "] "
"to sym=%p st_value=%08lx\n",
_get_rname(relotype),
addr, _get_val((uint16_t *)addr),
sym, sym->st_value);

/* NOTE: imm value for mv has been adjusted in previous HI20 */
offset = _find_hi20(arch_data, sym->st_value);

/* Adjust imm for MV(ADDI) / JR (JALR) : I-type */

_calc_imm(offset, &imm_hi, &imm_lo);

_add_val((uint16_t *)addr, (int32_t)imm_lo << 20);
}
break;

case R_RISCV_PCREL_HI20:
case R_RISCV_CALL:
case R_RISCV_CALL_PLT:
case R_RISCV_PCREL_LO12_S:
{
uint32_t val;
long imm_hi;
long imm_lo;

binfo("%s at %08" PRIxPTR " [%08" PRIx32 "] "
"to sym=%p st_value=%08lx\n",
_get_rname(relotype),
addr, _get_val((uint16_t *)addr),
sym, sym->st_value);

offset = (long)sym->st_value + (long)rel->r_addend - (long)addr;
offset = _find_hi20(arch_data, sym->st_value);

/* Adjust imm for SW : S-type */

_calc_imm(offset, &imm_hi, &imm_lo);

val = (((int32_t)imm_lo >> 5) << 25) +
(((int32_t)imm_lo & 0x1f) << 7);

binfo("imm_lo=%ld (%lx), val=%" PRIx32 "\n", imm_lo, imm_lo, val);

_add_val((uint16_t *)addr, val);
}
break;

case R_RISCV_PCREL_HI20:
{
long imm_hi;
long imm_lo;

binfo("%s at %08" PRIxPTR " [%08" PRIx32 "] "
"to sym=%p st_value=%08lx\n",
_get_rname(relotype),
addr, _get_val((uint16_t *)addr),
sym, sym->st_value);

offset = (long)sym->st_value + (long)rel->r_addend - (long)addr;

_calc_imm(offset, &imm_hi, &imm_lo);

/* Adjust auipc (add upper immediate to pc) : 20bit */

_add_val((uint16_t *)addr, (imm_hi << 12));
_add_val((uint16_t *)addr, imm_hi << 12);

if ((_get_val((uint16_t *)(addr + 4)) & 0x7f) == OPCODE_SW)
{
/* Adjust imm for SW : S-type */
/* Add the hi20 value to the cache */

uint32_t val =
(((int32_t)imm_lo >> 5) << 25) +
(((int32_t)imm_lo & 0x1f) << 7);
_add_hi20(arch_data, addr, offset);
}
break;

case R_RISCV_CALL:
case R_RISCV_CALL_PLT:
{
long imm_hi;
long imm_lo;

binfo("%s at %08" PRIxPTR " [%08" PRIx32 "] "
"to sym=%p st_value=%08lx\n",
_get_rname(relotype),
addr, _get_val((uint16_t *)addr),
sym, sym->st_value);

offset = (long)sym->st_value + (long)rel->r_addend - (long)addr;

_calc_imm(offset, &imm_hi, &imm_lo);

/* Adjust auipc (add upper immediate to pc) : 20bit */

binfo("imm_lo=%ld (%lx), val=%" PRIx32 "\n",
imm_lo, imm_lo, val);
_add_val((uint16_t *)addr, imm_hi << 12);

_add_val((uint16_t *)(addr + 4), val);
}
else
{
/* Adjust imm for MV(ADDI)/JALR : I-type */
/* Adjust imm for CALL (JALR) : I-type */

_add_val((uint16_t *)(addr + 4), ((int32_t)imm_lo << 20));
}
_add_val((uint16_t *)(addr + 4), (int32_t)imm_lo << 20);
}
break;

Expand Down

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