@@ -68,28 +68,45 @@ static void elfN(search_symtab)(ElfN(Shdr) *shdr, unsigned sym_idx,
void *buf, bool need_bswap)
{
unsigned str_idx = shdr[sym_idx].sh_link;
- ElfN(Sym) *sym = buf + shdr[sym_idx].sh_offset;
- unsigned sym_n = shdr[sym_idx].sh_size / sizeof(*sym);
+ ElfN(Sym) *target_sym = buf + shdr[sym_idx].sh_offset;
+ unsigned sym_n = shdr[sym_idx].sh_size / sizeof(*target_sym);
const char *str = buf + shdr[str_idx].sh_offset;
for (unsigned i = 0; i < sym_n; ++i) {
const char *name;
+ ElfN(Sym) sym;
+ memcpy(&sym, &target_sym[i], sizeof(sym));
if (need_bswap) {
- elfN(bswap_sym)(sym + i);
+ elfN(bswap_sym)(&sym);
}
- name = str + sym[i].st_name;
+ name = str + sym.st_name;
if (sigreturn_sym && strcmp(sigreturn_sym, name) == 0) {
- sigreturn_addr = sym[i].st_value;
+ sigreturn_addr = sym.st_value;
}
if (rt_sigreturn_sym && strcmp(rt_sigreturn_sym, name) == 0) {
- rt_sigreturn_addr = sym[i].st_value;
+ rt_sigreturn_addr = sym.st_value;
}
}
}
-static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
+static void elfN(bswap_ps_hdrs)(ElfN(Ehdr) *ehdr)
+{
+ ElfN(Phdr) *phdr = (void *)ehdr + ehdr->e_phoff;
+ ElfN(Shdr) *shdr = (void *)ehdr + ehdr->e_shoff;
+ ElfN(Half) i;
+
+ for (i = 0; i < ehdr->e_phnum; ++i) {
+ elfN(bswap_phdr)(&phdr[i]);
+ }
+
+ for (i = 0; i < ehdr->e_shnum; ++i) {
+ elfN(bswap_shdr)(&shdr[i]);
+ }
+}
+
+static void elfN(process)(FILE *outf, void *buf, long len, bool need_bswap)
{
ElfN(Ehdr) *ehdr = buf;
ElfN(Phdr) *phdr;
@@ -103,24 +120,14 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
int errors = 0;
if (need_bswap) {
- elfN(bswap_ehdr)(ehdr);
+ elfN(bswap_ehdr)(buf);
+ elfN(bswap_ps_hdrs)(buf);
}
phnum = ehdr->e_phnum;
phdr = buf + ehdr->e_phoff;
- if (need_bswap) {
- for (unsigned i = 0; i < phnum; ++i) {
- elfN(bswap_phdr)(phdr + i);
- }
- }
-
shnum = ehdr->e_shnum;
shdr = buf + ehdr->e_shoff;
- if (need_bswap) {
- for (unsigned i = 0; i < shnum; ++i) {
- elfN(bswap_shdr)(shdr + i);
- }
- }
for (unsigned i = 0; i < shnum; ++i) {
switch (shdr[i].sh_type) {
case SHT_SYMTAB:
@@ -154,7 +161,24 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
fprintf(stderr, "LOAD segment not loaded at address 0\n");
errors++;
}
- first_segsz = phdr[i].p_filesz;
+ /*
+ * Extend the program header to cover the entire VDSO, so that
+ * load_elf_vdso() loads everything, including section headers.
+ *
+ * Require that there is no .bss, since it would break this
+ * approach.
+ */
+ if (phdr[i].p_filesz != phdr[i].p_memsz) {
+ fprintf(stderr, "LOAD segment's filesz and memsz differ\n");
+ errors++;
+ }
+ if (phdr[i].p_filesz > len) {
+ fprintf(stderr, "LOAD segment is larger than the whole VDSO\n");
+ errors++;
+ }
+ phdr[i].p_filesz = len;
+ phdr[i].p_memsz = len;
+ first_segsz = len;
if (first_segsz < ehdr->e_phoff + phnum * sizeof(*phdr)) {
fprintf(stderr, "LOAD segment does not cover PHDRs\n");
errors++;
@@ -197,17 +221,24 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
output_reloc(outf, buf, &phdr[i].p_paddr);
}
+ /* Relocate the section headers. */
+ for (unsigned i = 0; i < shnum; ++i) {
+ output_reloc(outf, buf, &shdr[i].sh_addr);
+ }
+
/* Relocate the DYNAMIC entries. */
if (dynamic_addr) {
- ElfN(Dyn) *dyn = buf + dynamic_ofs;
- __typeof(dyn->d_tag) tag;
+ ElfN(Dyn) *target_dyn = buf + dynamic_ofs;
+ __typeof(((ElfN(Dyn) *)target_dyn)->d_tag) tag;
do {
+ ElfN(Dyn) dyn;
+ memcpy(&dyn, target_dyn, sizeof(dyn));
if (need_bswap) {
- elfN(bswap_dyn)(dyn);
+ elfN(bswap_dyn)(&dyn);
}
- tag = dyn->d_tag;
+ tag = dyn.d_tag;
switch (tag) {
case DT_HASH:
@@ -218,7 +249,7 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
case DT_PLTGOT:
case DT_ADDRRNGLO ... DT_ADDRRNGHI:
/* These entries store an address in the entry. */
- output_reloc(outf, buf, &dyn->d_un.d_val);
+ output_reloc(outf, buf, &target_dyn->d_un.d_val);
break;
case DT_NULL:
@@ -235,7 +266,7 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
break;
case DT_SYMENT:
- if (dyn->d_un.d_val != sizeof(ElfN(Sym))) {
+ if (dyn.d_un.d_val != sizeof(ElfN(Sym))) {
fprintf(stderr, "VDSO has incorrect dynamic symbol size\n");
errors++;
}
@@ -251,7 +282,7 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
* ??? The RISC-V toolchain will emit these even when there
* are no relocations. Validate zeros.
*/
- if (dyn->d_un.d_val != 0) {
+ if (dyn.d_un.d_val != 0) {
fprintf(stderr, "VDSO has dynamic relocations\n");
errors++;
}
@@ -287,7 +318,7 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
errors++;
break;
}
- dyn++;
+ target_dyn++;
} while (tag != DT_NULL);
if (errors) {
exit(EXIT_FAILURE);
@@ -296,11 +327,11 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
/* Relocate the dynamic symbol table. */
if (dynsym_idx) {
- ElfN(Sym) *sym = buf + shdr[dynsym_idx].sh_offset;
- unsigned sym_n = shdr[dynsym_idx].sh_size / sizeof(*sym);
+ ElfN(Sym) *target_sym = buf + shdr[dynsym_idx].sh_offset;
+ unsigned sym_n = shdr[dynsym_idx].sh_size / sizeof(*target_sym);
for (unsigned i = 0; i < sym_n; ++i) {
- output_reloc(outf, buf, &sym[i].st_value);
+ output_reloc(outf, buf, &target_sym[i].st_value);
}
}
@@ -311,4 +342,9 @@ static void elfN(process)(FILE *outf, void *buf, bool need_bswap)
if (symtab_idx) {
elfN(search_symtab)(shdr, symtab_idx, buf, need_bswap);
}
+
+ if (need_bswap) {
+ elfN(bswap_ps_hdrs)(buf);
+ elfN(bswap_ehdr)(buf);
+ }
}
@@ -131,23 +131,6 @@ int main(int argc, char **argv)
}
fclose(inf);
- /*
- * Write out the vdso image now, before we make local changes.
- */
-
- fprintf(outf,
- "/* Automatically generated from linux-user/gen-vdso.c. */\n"
- "\n"
- "static const uint8_t %s_image[] = {",
- prefix);
- for (long i = 0; i < total_len; ++i) {
- if (i % 12 == 0) {
- fputs("\n ", outf);
- }
- fprintf(outf, " 0x%02x,", buf[i]);
- }
- fprintf(outf, "\n};\n\n");
-
/*
* Identify which elf flavor we're processing.
* The first 16 bytes of the file are e_ident.
@@ -179,14 +162,17 @@ int main(int argc, char **argv)
* Output relocation addresses as we go.
*/
- fprintf(outf, "static const unsigned %s_relocs[] = {\n", prefix);
+ fprintf(outf,
+ "/* Automatically generated by linux-user/gen-vdso.c. */\n"
+ "\n"
+ "static const unsigned %s_relocs[] = {\n", prefix);
switch (buf[EI_CLASS]) {
case ELFCLASS32:
- elf32_process(outf, buf, need_bswap);
+ elf32_process(outf, buf, total_len, need_bswap);
break;
case ELFCLASS64:
- elf64_process(outf, buf, need_bswap);
+ elf64_process(outf, buf, total_len, need_bswap);
break;
default:
fprintf(stderr, "%s: invalid elf EI_CLASS (%u)\n",
@@ -196,6 +182,20 @@ int main(int argc, char **argv)
fprintf(outf, "};\n\n"); /* end vdso_relocs. */
+ /*
+ * Write out the vdso image now, after we made local changes.
+ */
+ fprintf(outf,
+ "static const uint8_t %s_image[] = {",
+ prefix);
+ for (long i = 0; i < total_len; ++i) {
+ if (i % 12 == 0) {
+ fputs("\n ", outf);
+ }
+ fprintf(outf, " 0x%02x,", buf[i]);
+ }
+ fprintf(outf, "\n};\n\n");
+
fprintf(outf, "static const VdsoImageInfo %s_image_info = {\n", prefix);
fprintf(outf, " .image = %s_image,\n", prefix);
fprintf(outf, " .relocs = %s_relocs,\n", prefix);
When debugging qemu-user processes using gdbstub, the following warning appears every time: warning: BFD: warning: system-supplied DSO at 0x7f8253cc3000 has a corrupt string table index The reason is that QEMU does not map the VDSO's section headers. The VDSO's ELF header's e_shoff points to zeros, which GDB fails to parse. The difference with the kernel's VDSO is that the latter is mapped as a blob, ignoring program headers - which also don't cover the section table. QEMU, on the other hand, loads it as an ELF file. There appears to be no way to place section headers inside a section, and, therefore, no way to refer to them from a linker script. Also, ld hardcodes section headers to be non-loadable, see _bfd_elf_assign_file_positions_for_non_load(). In theory ld could be enhanced by implementing an "SHDRS" keyword in addition to the existing "FILEHDR" and "PHDRS". There are multiple ways to resolve the issue: - Copy VDSO as a blob in load_elf_vdso(). This would require creating specialized loader logic, that duplicates parts of load_elf_image(). - Fix up VDSO's PHDR size in load_elf_vdso(). This would require either duplicating the parsing logic, or adding an ugly parameter to load_elf_image(). - Fix up VDSO's PHDR size in gen-vdso. This is the simplest solution, so do it. There are two tricky parts: - Byte-swaps need to be done either on local copies, or in-place and then reverted in the end. To preserve the existing code structure, do the former for Sym and Dyn, and the latter for Ehdr, Phdr, and Shdr. - There must be no .bss, which is already the case - but having an explicit check is helpful to ensure correctness. To verify this change, I diffed the on-disk and the loaded VDSOs; the result does not show anything unusual, except for what seems to be an existing oversight (which should probably be fixed separately): │ Symbol table '.dynsym' contains 8 entries: │ Num: Value Size Type Bind Vis Ndx Name │ - 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND │ - 6: 0000000000000000 0 OBJECT GLOBAL DEFAULT ABS LINUX_2.6.29 │ + 0: 00007f61075bf000 0 NOTYPE LOCAL DEFAULT UND │ + 6: 00007f61075bf000 0 OBJECT GLOBAL DEFAULT ABS LINUX_2.6.29 Fixes: 2fa536d10797 ("linux-user: Add gen-vdso tool") Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> --- v1: https://lore.kernel.org/qemu-devel/20241023144744.50440-1-iii@linux.ibm.com/ v1 -> v2: Check that there is no bss, mention linker scripts in the commit message (Richard). linux-user/gen-vdso-elfn.c.inc | 98 +++++++++++++++++++++++----------- linux-user/gen-vdso.c | 40 +++++++------- 2 files changed, 87 insertions(+), 51 deletions(-)