bpf, docs: Correct source of offset for program-local call

The offset to use when calculating the target of a program-local call is in the instruction's imm field, not its offset field. Signed-off-by: Will Hawkins <hawkinsw@obs.cr> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Eduard Zingerman <eddyz87@gmail.com> Acked-by: David Vernet <void@manifault.com> Link: https://lore.kernel.org/bpf/20230826053258.1860167-1-hawkinsw@obs.cr

Author: hawkinsw

Documentation/bpf/standardization/instruction-set.rst

@@ -373,7 +373,7 @@ BPF_JNE 0x5 any PC += offset if dst != src
 BPF_JSGT 0x6 any PC += offset if dst > src signed
 BPF_JSGE 0x7 any PC += offset if dst >= src signed
 BPF_CALL 0x8 0x0 call helper function by address see `Helper functions`_
-BPF_CALL 0x8 0x1 call PC += offset see `Program-local functions`_
+BPF_CALL 0x8 0x1 call PC += imm  see `Program-local functions`_
 BPF_CALL 0x8 0x2 call helper function by BTF ID see `Helper functions`_
 BPF_EXIT 0x9 0x0 return BPF_JMP only
 BPF_JLT 0xa any PC += offset if dst < src unsigned
@@ -424,8 +424,8 @@ Program-local functions
 ~~~~~~~~~~~~~~~~~~~~~~~
 Program-local functions are functions exposed by the same BPF program as the
 caller, and are referenced by offset from the call instruction, similar to
-``BPF_JA``. A ``BPF_EXIT`` within the program-local function will return to
-the caller.
+``BPF_JA``. The offset is encoded in the imm field of the call instruction.
+A ``BPF_EXIT`` within the program-local function will return to the caller.
 
 Load and store instructions
 ===========================