[PATCH 2/2] x86,vdso: Fix cross-compilation from big-endian architectures

Andy Lutomirski
2014-05-29T21:57:29Z

This adds a macro GET(x) to convert x from big-endian to
little-endian. Hopefully I put it everywhere it needs to go and got
all the cases needed for everyone's linux/elf.h.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---
arch/x86/vdso/vdso2c.c | 15 +++++++++++++
arch/x86/vdso/vdso2c.h | 59 ++++++++++++++++++++++++++++----------------------
2 files changed, 48 insertions(+), 26 deletions(-)

diff --git a/arch/x86/vdso/vdso2c.c b/arch/x86/vdso/vdso2c.c
index fe8bfbf..de19ced 100644
--- a/arch/x86/vdso/vdso2c.c
+++ b/arch/x86/vdso/vdso2c.c
@@ -51,6 +51,21 @@ static void fail(const char *format, ...)
va_end(ap);
}

+/*
+ * Evil macros to do a little-endian read.
+ */
+#define __GET_TYPE(x, type, bits, ifnot) \
+ __builtin_choose_expr( \
+ __builtin_types_compatible_p(typeof(x), type), \
+ le##bits##toh((x)), ifnot)
+
+extern void bad_get(uint64_t);
+
+#define GET(x) \
+ __GET_TYPE((x), __u32, 32, __GET_TYPE((x), __u64, 64, \
+ __GET_TYPE((x), __s32, 32, __GET_TYPE((x), __s64, 64, \
+ __GET_TYPE((x), __u16, 16, bad_get(x))))))
+
#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))

#define BITS 64
diff --git a/arch/x86/vdso/vdso2c.h b/arch/x86/vdso/vdso2c.h
index 26a7c1f..dadecb9 100644
--- a/arch/x86/vdso/vdso2c.h
+++ b/arch/x86/vdso/vdso2c.h
@@ -18,25 +18,27 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
const char *secstrings;
uint64_t syms[NSYMS] = {};

- Elf_Phdr *pt = (Elf_Phdr *)(addr + hdr->e_phoff);
+ Elf_Phdr *pt = (Elf_Phdr *)(addr + GET(hdr->e_phoff));

/* Walk the segment table. */
- for (i = 0; i < hdr->e_phnum; i++) {
- if (pt[i].p_type == PT_LOAD) {
+ for (i = 0; i < GET(hdr->e_phnum); i++) {
+ if (GET(pt[i].p_type) == PT_LOAD) {
if (found_load)
fail("multiple PT_LOAD segs\n");

- if (pt[i].p_offset != 0 || pt[i].p_vaddr != 0)
+ if (GET(pt[i].p_offset) != 0 ||
+ GET(pt[i].p_vaddr) != 0)
fail("PT_LOAD in wrong place\n");

- if (pt[i].p_memsz != pt[i].p_filesz)
+ if (GET(pt[i].p_memsz) != GET(pt[i].p_filesz))
fail("cannot handle memsz != filesz\n");

- load_size = pt[i].p_memsz;
+ load_size = GET(pt[i].p_memsz);
found_load = 1;
- } else if (pt[i].p_type == PT_DYNAMIC) {
- dyn = addr + pt[i].p_offset;
- dyn_end = addr + pt[i].p_offset + pt[i].p_memsz;
+ } else if (GET(pt[i].p_type) == PT_DYNAMIC) {
+ dyn = addr + GET(pt[i].p_offset);
+ dyn_end = addr + GET(pt[i].p_offset) +
+ GET(pt[i].p_memsz);
}
}
if (!found_load)
@@ -44,43 +46,48 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
data_size = (load_size + 4095) / 4096 * 4096;

/* Walk the dynamic table */
- for (i = 0; dyn + i < dyn_end && dyn[i].d_tag != DT_NULL; i++) {
- if (dyn[i].d_tag == DT_REL || dyn[i].d_tag == DT_RELSZ ||
- dyn[i].d_tag == DT_RELENT || dyn[i].d_tag == DT_TEXTREL)
+ for (i = 0; dyn + i < dyn_end && GET(dyn[i].d_tag) != DT_NULL; i++) {
+ typeof(dyn[i].d_tag) tag = GET(dyn[i].d_tag);
+ if (tag == DT_REL || tag == DT_RELSZ ||
+ tag == DT_RELENT || tag == DT_TEXTREL)
fail("vdso image contains dynamic relocations\n");
}

/* Walk the section table */
- secstrings_hdr = addr + hdr->e_shoff + hdr->e_shentsize*hdr->e_shstrndx;
- secstrings = addr + secstrings_hdr->sh_offset;
- for (i = 0; i < hdr->e_shnum; i++) {
- Elf_Shdr *sh = addr + hdr->e_shoff + hdr->e_shentsize * i;
- if (sh->sh_type == SHT_SYMTAB)
+ secstrings_hdr = addr + GET(hdr->e_shoff) +
+ GET(hdr->e_shentsize)*GET(hdr->e_shstrndx);
+ secstrings = addr + GET(secstrings_hdr->sh_offset);
+ for (i = 0; i < GET(hdr->e_shnum); i++) {
+ Elf_Shdr *sh = addr + GET(hdr->e_shoff) +
+ GET(hdr->e_shentsize) * i;
+ if (GET(sh->sh_type) == SHT_SYMTAB)
symtab_hdr = sh;

- if (!strcmp(secstrings + sh->sh_name, ".altinstructions"))
+ if (!strcmp(secstrings + GET(sh->sh_name), ".altinstructions"))
alt_sec = sh;
}

if (!symtab_hdr)
fail("no symbol table\n");

- strtab_hdr = addr + hdr->e_shoff +
- hdr->e_shentsize * symtab_hdr->sh_link;
+ strtab_hdr = addr + GET(hdr->e_shoff) +
+ GET(hdr->e_shentsize) * GET(symtab_hdr->sh_link);

/* Walk the symbol table */
- for (i = 0; i < symtab_hdr->sh_size / symtab_hdr->sh_entsize; i++) {
+ for (i = 0; i < GET(symtab_hdr->sh_size) / GET(symtab_hdr->sh_entsize);
+ i++) {
int k;
- Elf_Sym *sym = addr + symtab_hdr->sh_offset +
- symtab_hdr->sh_entsize * i;
- const char *name = addr + strtab_hdr->sh_offset + sym->st_name;
+ Elf_Sym *sym = addr + GET(symtab_hdr->sh_offset) +
+ GET(symtab_hdr->sh_entsize) * i;
+ const char *name = addr + GET(strtab_hdr->sh_offset) +
+ GET(sym->st_name);
for (k = 0; k < NSYMS; k++) {
if (!strcmp(name, required_syms[k])) {
if (syms[k]) {
fail("duplicate symbol %s\n",
required_syms[k]);
}
- syms[k] = sym->st_value;
+ syms[k] = GET(sym->st_value);
}
}
}
@@ -106,7 +113,7 @@ static void GOFUNC(void *addr, size_t len, FILE *outfile, const char *name)
hdr->e_shoff = 0;
hdr->e_shentsize = 0;
hdr->e_shnum = 0;
- hdr->e_shstrndx = SHN_UNDEF;
+ hdr->e_shstrndx = htole16(SHN_UNDEF);

if (!name) {
fwrite(addr, load_size, 1, outfile);
--
1.9.3