[PATCH] ARM: Identify the hard-float ABI in older ARM binaries

[Steve McIntyre <steve.mcintyre@linaro.org>]

Hi,

I expect this one to be more controversial and I'll understand if
people don't want to accept it! It's a variation on the code that's in
use today in Debian/Ubuntu to be able to distinguish between soft- and
hard-float ABI libraries. In time, the new ELF flags will make this
obsolete. Until that time, this adds a fallback for older binaries
created before those flags went into binutils.

==============================
Identify the hard-float ABI in older ARM binaries

	* ports/sysdeps/unix/sysv/linux/arm/readelflib.c (read_uleb128):
	New function.
	(is_library_hf): Ditto.
	(process_elf_file): Call is_library_hf() to detect HF ABI if
	we don't have clear evidence from the ELF flags.

Signed-off-by: Steve McIntyre <steve.mcintyre@linaro.org>
---
 ports/sysdeps/unix/sysv/linux/arm/readelflib.c |  129 ++++++++++++++++++++++++
 1 file changed, 129 insertions(+)

diff --git a/ports/sysdeps/unix/sysv/linux/arm/readelflib.c b/ports/sysdeps/unix/sysv/linux/arm/readelflib.c
index e4ba2b0..0287644 100644
--- a/ports/sysdeps/unix/sysv/linux/arm/readelflib.c
+++ b/ports/sysdeps/unix/sysv/linux/arm/readelflib.c
@@ -25,6 +25,133 @@ int process_elf64_file (const char *file_name, const char *lib, int *flag,
 			unsigned int *osversion, char **soname,
 			void *file_contents, size_t file_length);
 
+#undef __ELF_NATIVE_CLASS
+#define __ELF_NATIVE_CLASS 32
+
+/* Read an unsigned leb128 value from P, store the value in VAL, return
+   P incremented past the value.  We assume that a word is large enough to
+   hold any value so encoded; if it is smaller than a pointer on some target,
+   pointers should not be leb128 encoded on that target.  */
+static const unsigned char *
+read_uleb128 (const unsigned char *p, unsigned long *val)
+{
+  unsigned int shift = 0;
+  unsigned char byte;
+  unsigned long result;
+
+  result = 0;
+  do
+    {
+      byte = *p++;
+      result |= (byte & 0x7f) << shift;
+      shift += 7;
+    }
+  while (byte & 0x80);
+
+  *val = result;
+  return p;
+}
+
+#define ATTR_TAG_FILE          1
+#define ABI_VFP_args          28
+#define VFP_ARGS_IN_VFP_REGS   1
+
+/* Check the ABI in the ARM attributes. Search through the section
+   headers looking for the ARM attributes section, then check the
+   VFP_ARGS attribute. */
+static int is_library_hf(const char *file_name, void *file_contents, size_t file_length)
+{
+  unsigned int i;
+  ElfW(Ehdr) *ehdr = (ElfW(Ehdr) *) file_contents;
+  ElfW(Shdr) *shdrs;
+
+  shdrs = file_contents + ehdr->e_shoff;
+  for (i = 0; i < ehdr->e_shnum; i++)
+    {
+      if (SHT_ARM_ATTRIBUTES == shdrs[i].sh_type)
+	{
+          /* We've found a likely section. Load the contents and
+           * check the tags */
+	  unsigned char *p = (unsigned char *)file_contents + shdrs[i].sh_offset;
+	  unsigned char * end;
+
+	  /* Sanity-check the attribute section details. Make sure
+	   * that it's the "aeabi" section, that's all we care
+	   * about. */
+	  if (*p == 'A')
+	    {
+	      unsigned long len = shdrs[i].sh_size - 1;
+	      unsigned long namelen;
+	      p++;
+
+	      while (len > 0)
+		{
+		  unsigned long section_len = p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+		  if (section_len > len)
+		    section_len = len;
+
+		  p += 4;
+		  len -= section_len;
+		  section_len -= 4;
+
+		  if (0 != strcmp((char *)p, "aeabi"))
+		    {
+		      p += section_len;
+		      continue;
+		    }
+		  namelen = strlen((char *)p) + 1;
+		  p += namelen;
+		  section_len -= namelen;
+
+		  /* We're in a valid section. Walk through this
+		   * section looking for the tag we care about
+		   * (ABI_VFP_args) */
+		  while (section_len > 0)
+                    {
+		      unsigned long tag, val = 0;
+		      unsigned long size;
+
+		      end = p;
+		      tag = (*p++);
+		      size = p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+		      if (size > section_len)
+			size = section_len;
+		      p += 4;
+
+		      section_len -= size;
+		      end += size;
+		      if (ATTR_TAG_FILE != tag)
+			{
+			  /* ignore, we don't care */
+			  p = end;
+			  continue;
+			}
+		      while (p < end)
+		        {
+			  p = read_uleb128 (p, &tag);
+			  /* Handle the different types of tag. */
+			  if ( (tag == 4) || (tag == 5) || (tag == 67) )
+			    {
+			      /* Special cases for string values */
+			      namelen = strlen((char *)p) + 1;
+			      p += namelen;
+                            }
+			  else
+			    {
+			      p = read_uleb128 (p, &val);
+                            }
+			  if ( (tag == ABI_VFP_args) && (val == VFP_ARGS_IN_VFP_REGS) )
+			    return 1;
+                        }
+                    }
+                }
+            }
+        }
+    }
+  return 0;
+}
+
+
 /* Returns 0 if everything is ok, != 0 in case of error.  */
 int
 process_elf_file (const char *file_name, const char *lib, int *flag,
@@ -47,6 +174,8 @@ process_elf_file (const char *file_name, const char *lib, int *flag,
 	    *flag = FLAG_ARM_LIBHF|FLAG_ELF_LIBC6;
 	  else if (elf32_header->e_flags & EF_ARM_ABI_FLOAT_SOFT)
 	    *flag = FLAG_ELF_LIBC6;
+	  else if (is_library_hf(file_name, file_contents, file_length))
+	    *flag = FLAG_ARM_LIBHF|FLAG_ELF_LIBC6;
 	}
     }
   else
-- 
1.7.10.4



Cheers,
-- 
Steve McIntyre                                steve.mcintyre@linaro.org
<http://www.linaro.org/> Linaro.org | Open source software for ARM SoCs