Expose the buildid hash through sysctl

[ali_mashtizadeh.com]

Summary

Exposes the buildid hash through sysctl and adds uname -b to display the buildid

Test Plan

check output using uname and sysctl

[rpokala]

sys/kern/kern_mib.c

501

Please explain the magic number. Or, better still, #define it and put the explanation there.

[jhb]

Just to be clear, this doesn't compile yet on !amd64? Also, does uname -a still work for a kernel built without build-id?

sys/kern/kern_mib.c

491

Does this link if you don't have build-id support in the linker?

[emaste]

will also want a uname.3 update

sys/kern/kern_mib.c

519

let's make this kern.build_id, buildid parses as "buil did" for me

521

build-id

[ali_mashtizadeh.com]

• Updates and linker scripts for other archs

[emaste]

sys/kern/kern_mib.c

501

trying strange build-id sizes - % cc -Wl,--build-id=0x1234 hello.c

file does not report the build-id at all:

% file a.out
a.out: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 12.0 (1200085), FreeBSD-style, with debug_info, not stripped

but readelf shows that it's there:

% readelf -n a.out

Notes at offset 0x000002c0 with length 0x00000048:
  Owner         Data size       Description
  FreeBSD       0x00000004      NT_FREEBSD_ABI_TAG
  FreeBSD       0x00000004      NT_FREEBSD_FEATURE_CTL
  FreeBSD       0x00000004      NT_FREEBSD_NOINIT_TAG

Notes at offset 0x00000310 with length 0x00000012:
  Owner         Data size       Description
  GNU           0x00000002      NT_GNU_BUILD_ID (Build id set by ld(1))

my lld defaults to 8-byte xxHash:

% cc -Wl,--build-id hello.c      
% file a.out               
a.out: ELF 64-bit LSB executable, x86-64, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 12.0 (1200085), FreeBSD-style, BuildID[xxHash]=7bda57f23f3db219, with debug_info, not stripped

I think we can assume it will be one of 8, 16, or 20 bytes long though.

[ali_mashtizadeh.com]

sys/kern/kern_mib.c

491

In the updated diff I fix all linker scripts. This will show up as an empty section.

[ali_mashtizadeh.com]

• Addresses Ed Maste's feedback. This change allows the sysctl to return any build-id between 1 and 20 bytes.

[ali_mashtizadeh.com]

Sample output:
root@skylake8:~ # uname -a
FreeBSD skylake8.rcs.uwaterloo.ca 13.0-CURRENT FreeBSD 13.0-CURRENT #9 da147860ca7(master)-dirty: Mon May 20 17:32:20 EDT 2019 [e-mail]:/build/ali/obj/working/freebsd-dev/amd64.amd64/sys/GENERIC amd64 42e907d740dd9560a2dfd7187eee20e41e9fbd9f
root@skylake8:~ # uname -b
42e907d740dd9560a2dfd7187eee20e41e9fbd9f

[emaste]

In D20326#438264, @ali_mashtizadeh.com wrote:

Sample output:
root@skylake8:~ # uname -a
FreeBSD skylake8.rcs.uwaterloo.ca 13.0-CURRENT FreeBSD 13.0-CURRENT #9 da147860ca7(master)-dirty: Mon May 20 17:32:20 EDT 2019 [e-mail]:/build/ali/obj/working/freebsd-dev/amd64.amd64/sys/GENERIC amd64 42e907d740dd9560a2dfd7187eee20e41e9fbd9f

I worry that there are tools parsing uname -a and will be confused by the extra output. Maybe we should commit the kernel changes first and ask for an exp-run (and broader user testing) on the uname changes.

[ali_mashtizadeh.com]

• Update man page and remove from -a

[ali_mashtizadeh.com]

• Adding defines

[ali_mashtizadeh.com]

Tinderbox passed

[rpokala]

sys/kern/kern_mib.c

494

May I suggest that you move the comment about the header here, where the value is defined? i.e.

	/* The ELF note section has a four byte length for the vendor name,
	 * four byte length for the value, and a four byte vendor specific 
	 * type.  The name for the build id is "GNU\0".  We skip the first 16 
	 * bytes to read the build hash.
	 */

495

And similarly, move the length comment here as well:

	/* 20 (SHA-1) hash size */

509

If you move the comments to the definitions as I suggest above, this becomes

	/* Return the remaining bytes up to the hash size. If the hash
	 * happens to be a custom number of bytes, we will pad the
	 * value with zeros, as the section should be four-byte aligned.
	 */

(with whatever appropriate wrapping, of course)

[emaste]

I will pick up whitespace cleanup, .Dd bump etc. for commit

usr.bin/uname/uname.1

31

will update .Dd upon commit

57

maybe linker-generated kernel build-id? As is seems to suggest that this is some ID of the linker itself.

[emaste]

I will commit the uname changes separately