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s390/bug: Implement __WARN_printf()

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This is the s390 variant of commit 5b472b6e5b ("x86_64/bug: Implement
__WARN_printf()"). See the x86 commit for the general idea; there are only
implementation details which are different.

With the new exception based __WARN_printf() implementation the generated
code for a simple WARN() is simplified.

For example:

void foo(int a) { WARN(a, "bar"); }

Before this change the generated code looks like this:

0000000000000210 <foo>:
 210:   c0 04 00 00 00 00       jgnop   210 <foo>
 216:   ec 26 00 06 00 7c       cgijne  %r2,0,222 <foo+0x12>
 21c:   c0 f4 00 00 00 00       jg      21c <foo+0xc>
                        21e: R_390_PC32DBL      __s390_indirect_jump_r14+0x2
 222:   eb ef f0 88 00 24       stmg    %r14,%r15,136(%r15)
 228:   b9 04 00 ef             lgr     %r14,%r15
 22c:   e3 f0 ff e8 ff 71       lay     %r15,-24(%r15)
 232:   e3 e0 f0 98 00 24       stg     %r14,152(%r15)
 238:   c0 20 00 00 00 00       larl    %r2,238 <foo+0x28>
                        23a: R_390_PC32DBL      .LC48+0x2
 23e:   c0 e5 00 00 00 00       brasl   %r14,23e <foo+0x2e>
                        240: R_390_PLT32DBL     __warn_printk+0x2
 244:   af 00 00 00             mc      0,0
 248:   eb ef f0 a0 00 04       lmg     %r14,%r15,160(%r15)
 24e:   c0 f4 00 00 00 00       jg      24e <foo+0x3e>
                        250: R_390_PC32DBL      __s390_indirect_jump_r14+0x2

With this change the generated code looks like this:

0000000000000210 <foo>:
 210:   c0 04 00 00 00 00       jgnop   210 <foo>
 216:   ec 26 00 06 00 7c       cgijne  %r2,0,222 <foo+0x12>
 21c:   c0 f4 00 00 00 00       jg      21c <foo+0xc>
                        21e: R_390_PC32DBL      __s390_indirect_jump_r14+0x2
 222:   c0 20 00 00 00 00       larl    %r2,222 <foobar+0x12>
                        224: R_390_PC32DBL      __bug_table+0x2
 228:   c0 f4 00 00 00 00       jg      228 <foobar+0x18>
                        22a: R_390_PLT32DBL     __WARN_trap+0x2

Downside is that the call trace now starts at __WARN_trap():

------------[ cut here ]------------
bar
WARNING: arch/s390/kernel/setup.c:1017 at 0x0, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe0f6a3b4 (__WARN_trap+0x4/0x10)
...
Krnl Code: 000003ffe0f6a3ac: 0707                bcr     0,%r7
           000003ffe0f6a3ae: 0707                bcr     0,%r7
          *000003ffe0f6a3b0: af000001            mc      1,0
          >000003ffe0f6a3b4: 07fe                bcr     15,%r14
           000003ffe0f6a3b6: 47000700            bc      0,1792
           000003ffe0f6a3ba: 0707                bcr     0,%r7
           000003ffe0f6a3bc: 0707                bcr     0,%r7
           000003ffe0f6a3be: 0707                bcr     0,%r7
Call Trace:
 [<000003ffe0f6a3b4>] __WARN_trap+0x4/0x10
([<000003ffe185a54c>] start_kernel+0x53c/0x5d8)
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Which isn't too helpful. This can be addressed by just skipping __WARN_trap(),
which will be addressed in a later patch.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2026-01-09 16:31:41 +01:00
parent ee44f4e7eb
commit 04dabb4261
4 changed files with 105 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

1
arch/s390/include/asm/asm-prototypes.h
View file

@ -3,6 +3,7 @@
#include <linux/kvm_host.h>
#include <linux/ftrace.h>
#include <asm/bug.h>
#include <asm/fpu.h>
#include <asm/nospec-branch.h>
#include <asm-generic/asm-prototypes.h>

62
arch/s390/include/asm/bug.h
View file

@ -6,6 +6,7 @@
#include <linux/const.h>
#define MONCODE_BUG _AC(0, U)
#define MONCODE_BUG_ARG _AC(1, U)
#ifndef __ASSEMBLER__
#if defined(CONFIG_BUG) && defined(CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS)
@ -25,16 +26,20 @@
#define WARN_CONDITION_STR(cond_str) ""
#endif
#define __BUG_ENTRY(format, file, line, flags, size) \
" .section __bug_table,\"aw\"\n" \
"1: .long 0b - . # bug_entry::bug_addr\n" \
__BUG_ENTRY_VERBOSE(format, file, line) \
" .short "flags" # bug_entry::flags\n" \
" .org 1b+"size"\n" \
" .previous"
#define __BUG_ASM(cond_str, flags) \
do { \
asm_inline volatile("\n" \
"0: mc %[monc](%%r0),0\n" \
" .section __bug_table,\"aw\"\n" \
"1: .long 0b - . # bug_entry::bug_addr\n" \
__BUG_ENTRY_VERBOSE("%[frmt]", "%[file]", "%[line]") \
" .short %[flgs] # bug_entry::flags\n" \
" .org 1b+%[size]\n" \
" .previous" \
__BUG_ENTRY("%[frmt]", "%[file]", "%[line]", \
"%[flgs]", "%[size]") \
: \
: [monc] "i" (MONCODE_BUG), \
[frmt] "i" (WARN_CONDITION_STR(cond_str)), \
@ -55,8 +60,53 @@ do { \
__BUG_ASM(cond_str, BUGFLAG_WARNING | (flags)); \
} while (0)
#define __WARN_bug_entry(flags, format) \
({ \
struct bug_entry *bug; \
\
asm_inline volatile("\n" \
"0: larl %[bug],1f\n" \
__BUG_ENTRY("%[frmt]", "%[file]", "%[line]", \
"%[flgs]", "%[size]") \
: [bug] "=d" (bug) \
: [frmt] "i" (format), \
[file] "i" (__FILE__), \
[line] "i" (__LINE__), \
[flgs] "i" (flags), \
[size] "i" (sizeof(struct bug_entry))); \
bug; \
})
/*
* Variable Argument List (va_list) as defined in ELF Application
* Binary Interface s390x Supplement documentation.
*/
struct arch_va_list {
long __gpr;
long __fpr;
void *__overflow_arg_area;
void *__reg_save_area;
};
struct bug_entry;
struct pt_regs;
void *__warn_args(struct arch_va_list *args, struct pt_regs *regs);
void __WARN_trap(struct bug_entry *bug, ...);
#define __WARN_print_arg(flags, format, arg...) \
do { \
int __flags = (flags) | BUGFLAG_WARNING | BUGFLAG_ARGS; \
\
__WARN_trap(__WARN_bug_entry(__flags, format), ## arg); \
} while (0)
#define __WARN_printf(taint, fmt, arg...) \
__WARN_print_arg(BUGFLAG_TAINT(taint), fmt, ## arg)
#define HAVE_ARCH_BUG
#define HAVE_ARCH_BUG_FORMAT
#define HAVE_ARCH_BUG_FORMAT_ARGS
#endif /* CONFIG_BUG && CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS */
#endif /* __ASSEMBLER__ */

11
arch/s390/kernel/entry.S
View file

@ -23,6 +23,7 @@
#include <asm/unistd.h>
#include <asm/page.h>
#include <asm/sigp.h>
#include <asm/bug.h>
#include <asm/irq.h>
#include <asm/fpu-insn.h>
#include <asm/setup.h>
@ -173,6 +174,16 @@ SYM_FUNC_START(__switch_to_asm)
BR_EX %r14
SYM_FUNC_END(__switch_to_asm)
#if defined(CONFIG_BUG) && defined(CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS)
SYM_FUNC_START(__WARN_trap)
mc MONCODE_BUG_ARG(%r0),0
BR_EX %r14
SYM_FUNC_END(__WARN_trap)
EXPORT_SYMBOL(__WARN_trap)
#endif /* CONFIG_BUG && CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS */
#if IS_ENABLED(CONFIG_KVM)
/*
* __sie64a calling convention:

38
arch/s390/kernel/traps.c
View file

@ -23,6 +23,7 @@
#include <linux/cpu.h>
#include <linux/entry-common.h>
#include <linux/kmsan.h>
#include <linux/bug.h>
#include <asm/asm-extable.h>
#include <asm/irqflags.h>
#include <asm/ptrace.h>
@ -220,11 +221,46 @@ static void space_switch_exception(struct pt_regs *regs)
do_trap(regs, SIGILL, ILL_PRVOPC, "space switch event");
}
#if defined(CONFIG_BUG) && defined(CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS)
void *__warn_args(struct arch_va_list *args, struct pt_regs *regs)
{
struct stack_frame *stack_frame;
/*
* Generate va_list from pt_regs. See ELF Application Binary Interface
* s390x Supplement documentation for details.
*
* - __overflow_arg_area needs to point to the parameter area, which
* is right above the standard stack frame (160 bytes)
*
* - __reg_save_area needs to point to a register save area where
* general registers (%r2 - %r6) can be found at offset 16. Which
* means that the gprs save area of pt_regs can be used
*
* - __gpr must be set to one, since the first parameter has been
* processed (pointer to bug_entry)
*/
stack_frame = (struct stack_frame *)regs->gprs[15];
args->__overflow_arg_area = stack_frame + 1;
args->__reg_save_area = regs->gprs;
args->__gpr = 1;
return args;
}
#endif /* CONFIG_BUG && CONFIG_CC_HAS_ASM_IMMEDIATE_STRINGS */
static void monitor_event_exception(struct pt_regs *regs)
{
enum bug_trap_type btt;
if (user_mode(regs))
return;
switch (report_bug(regs->psw.addr - (regs->int_code >> 16), regs)) {
if (regs->monitor_code == MONCODE_BUG_ARG)
btt = report_bug_entry((struct bug_entry *)regs->gprs[2], regs);
else
btt = report_bug(regs->psw.addr - (regs->int_code >> 16), regs);
switch (btt) {
case BUG_TRAP_TYPE_NONE:
fixup_exception(regs);
break;