[PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ and __global_pointer$ on riscv

[PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ and __global_pointer$ on riscv

[Andreas Schwab]

Signed-off-by: Andreas Schwab <schwab@suse.de>
---
 backends/ChangeLog      |  5 +++++
 backends/riscv_init.c   |  1 +
 backends/riscv_symbol.c | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/backends/ChangeLog b/backends/ChangeLog
index 63bb7e444e..0dde0ff3f5 100644
--- a/backends/ChangeLog
+++ b/backends/ChangeLog
@@ -1,3 +1,8 @@
+2018-05-15  Andreas Schwab  <schwab@suse.de>
+
+	* riscv_init.c (riscv_init): Hook check_special_symbol.
+	* riscv_symbol.c (riscv_check_special_symbol): New function.
+
 2018-04-19  Andreas Schwab  <schwab@suse.de>
 
 	* Makefile.am (modules): Add riscv.
diff --git a/backends/riscv_init.c b/backends/riscv_init.c
index 0203eac8b8..4234cded2b 100644
--- a/backends/riscv_init.c
+++ b/backends/riscv_init.c
@@ -52,6 +52,7 @@ riscv_init (Elf *elf __attribute__ ((unused)),
   riscv_init_reloc (eh);
   HOOK (eh, register_info);
   HOOK (eh, reloc_simple_type);
+  HOOK (eh, check_special_symbol);
   HOOK (eh, machine_flag_check);
 
   return MODVERSION;
diff --git a/backends/riscv_symbol.c b/backends/riscv_symbol.c
index 628e0572ae..dce8e3586b 100644
--- a/backends/riscv_symbol.c
+++ b/backends/riscv_symbol.c
@@ -60,3 +60,35 @@ riscv_machine_flag_check (GElf_Word flags)
   return ((flags &~ (EF_RISCV_RVC
 		     | EF_RISCV_FLOAT_ABI)) == 0);
 }
+
+/* Check whether given symbol's st_value and st_size are OK despite failing
+   normal checks.  */
+bool
+riscv_check_special_symbol (Elf *elf, GElf_Ehdr *ehdr, const GElf_Sym *sym,
+			    const char *name, const GElf_Shdr *destshdr)
+{
+  if (name == NULL)
+    return false;
+
+  const char *sname = elf_strptr (elf, ehdr->e_shstrndx, destshdr->sh_name);
+  if (sname == NULL)
+    return false;
+
+  /* _GLOBAL_OFFSET_TABLE_ points to the start of the .got section, but it
+     is preceded by the .got.plt section in the output .got section.  */
+  if (strcmp (name, "_GLOBAL_OFFSET_TABLE_") == 0)
+    return (strcmp (sname, ".got") == 0
+	    && sym->st_value >= destshdr->sh_addr
+	    && sym->st_value < destshdr->sh_addr + destshdr->sh_size);
+
+  /* __global_pointer$ points to the .sdata section with an offset of
+     0x800.  It might however fall in the .got section, in which case we
+     cannot check the offset.  The size always should be zero.  */
+  if (strcmp (name, "__global_pointer$") == 0)
+    return (((strcmp (sname, ".sdata") == 0
+	      && sym->st_value == destshdr->sh_addr + 0x800)
+	     || strcmp (sname, ".got") == 0)
+	    && sym->st_size == 0);
+
+  return false;
+}
-- 
2.17.0


-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: [PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ and __global_pointer$ on riscv

[Mark Wielaard]

On Tue, 2018-05-15 at 13:47 +0200, Andreas Schwab wrote:
> +
> +	* riscv_init.c (riscv_init): Hook check_special_symbol.
> +	* riscv_symbol.c (riscv_check_special_symbol): New function.

Looks good. Pushed.

I assume this solves some of the self-tests in make check on riscv.

Is there an ELF abi document for riscv that describes these special
symbols?

Thanks,

Mark

Re: [PATCH] backends: add checks for _GLOBAL_OFFSET_TABLE_ and __global_pointer$ on riscv

[Andreas Schwab]

On Mai 15 2018, Mark Wielaard <mark@klomp.org> wrote:

> Is there an ELF abi document for riscv that describes these special
> symbols?

There is
<https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md>,
but it doesn't mention the symbols.  I have extracted that out of the
binutils sources.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."