Re: [PATCH v6 3/7] ftrace: Add arm64 support to recordmcount

On 03/13/2014 09:38 PM, Will Deacon wrote:

On Thu, Mar 13, 2014 at 10:13:46AM +0000, AKASHI Takahiro wrote:

...

Recordmcount utility under scripts is run, after compiling each object, to find out all the locations of calling _mcount() and put them into specific seciton named __mcount_loc. Then linker collects all such information into a table in the kernel image (between __start_mcount_loc and __stop_mcount_loc) for later use by ftrace.

This patch adds arm64 specific definitions to identify such locations. There are two types of implementation, C and Perl. On arm64, only C version is used to build the kernel now that CONFIG_HAVE_C_RECORDMCOUNT is on. But Perl version is also maintained.

This patch also contains a workaround just in case where a header file, elf.h, on host machine doesn't have definitions of EM_AARCH64 nor R_AARCH64_ABS64. Without them, compiling C version of recordmcount will fail.

[...]

...

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c index 9c22317..047c8cd 100644 --- a/scripts/recordmcount.c +++ b/scripts/recordmcount.c @@ -40,6 +40,11 @@ #define R_METAG_NONE 3 #endif

+#ifndef EM_AARCH64 +#define EM_AARCH64 183 +#define R_AARCH64_ABS64 257 +#endif

• static int fd_map; /* File descriptor for file being modified. */ static int mmap_failed; /* Boolean flag. */ static void *ehdr_curr; /* current ElfXX_Ehdr * for resource cleanup */

@@ -347,6 +352,10 @@ do_file(char const *const fname) case EM_ARM: reltype = R_ARM_ABS32; altmcount = "__gnu_mcount_nc"; break;

• case EM_AARCH64:

• 	 reltype = R_AARCH64_ABS64;
  

• 	 altmcount = "_mcount";
  

Shouldn't you be setting gpfx = '_' instead of overriding altmcount like this?

Yep. Fix it.

...

• 	 break;
  

  case EM_IA_64: reltype = R_IA64_IMM64; gpfx = '_'; break; case EM_METAG: reltype = R_METAG_ADDR32; altmcount = "_mcount_wrapper";

diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl index 91280b8..397b6b8 100755 --- a/scripts/recordmcount.pl +++ b/scripts/recordmcount.pl @@ -279,6 +279,11 @@ if ($arch eq "x86_64") { $mcount_regex = "^\s*([0-9a-fA-F]+):\s*R_ARM_(CALL|PC24|THM_CALL)" . "\s+(__gnu_mcount_nc|mcount)$";

+} elsif ($arch eq "arm64") {

• $alignment = 3;
• $section_type = '%progbits';
• $mcount_regex = "^\s*([0-9a-fA-F]+):\s*R_AARCH64_CALL26\s+_mcount$";

What about "mcount" (i.e. no underscore)?

I don't think it works since such regex doesn't match to "CALL26 _mcount".

Thanks, -Takahiro AKASHI

Will