kallsyms: remove unused arch_get_kallsym() helper

The arch_get_kallsym() function was introduced so that x86 could override
it, but that override was removed in bf904d2762ee ("x86/pti/64: Remove
the SYSCALL64 entry trampoline"), so now this does nothing except causing
a warning about a missing prototype:

kernel/kallsyms.c:662:12: error: no previous prototype for 'arch_get_kallsym' [-Werror=missing-prototypes]
662 | int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,

Restore the old behavior before d83212d5dd67 ("kallsyms, x86: Export
addresses of PTI entry trampolines") to simplify the code and avoid
the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
[mcgrof: fold in bpf selftest fix]
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

selftests/bpf: fix lots of silly mistakes pointed out by compiler

Once we enable -Wall for BPF sources, compiler will complain about lots
of unused variables, variables that are set but never read, etc.

Fix all these issues first before enabling -Wall in Makefile.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230309054015.4068562-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Fix conflicts with built-in functions in bpf_iter_ksym

Both tolower and toupper are built in c functions, we should not
redefine them as this can result in a build error.

Fixes the following errors:
progs/bpf_iter_ksym.c:10:20: error: conflicting types for built-in function 'tolower'; expected 'int(int)' [-Werror=builtin-declaration-mismatch]
10 | static inline char tolower(char c)
| ^~~~~~~
progs/bpf_iter_ksym.c:5:1: note: 'tolower' is declared in header '<ctype.h>'
4 | #include <bpf/bpf_helpers.h>
+++ |+#include <ctype.h>
5 |
progs/bpf_iter_ksym.c:17:20: error: conflicting types for built-in function 'toupper'; expected 'int(int)' [-Werror=builtin-declaration-mismatch]
17 | static inline char toupper(char c)
| ^~~~~~~
progs/bpf_iter_ksym.c:17:20: note: 'toupper' is declared in header '<ctype.h>'

See background on this sort of issue:
https://stackoverflow.com/a/20582607
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=12213

(C99, 7.1.3p1) "All identifiers with external linkage in any of the
following subclauses (including the future library directions) are
always reserved for use as identifiers with external linkage."

This is documented behavior in GCC:
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-std-2

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221203010847.2191265-1-james.hilliard1@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: add a ksym iter subtest

add subtest verifying BPF ksym iter behaviour. The BPF ksym
iter program shows an example of dumping a format different to
/proc/kallsyms. It adds KIND and MAX_SIZE fields which represent the
kind of symbol (core kernel, module, ftrace, bpf, or kprobe) and
the maximum size the symbol can be. The latter is calculated from
the difference between current symbol value and the next symbol
value.

The key benefit for this iterator will likely be supporting in-kernel
data-gathering rather than dumping symbol details to userspace and
parsing the results.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/1657629105-7812-3-git-send-email-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>