[Crash-utility] Re: [PATCH] x86_64: Fix "bt" command for noreturn functions

Hi Kazu, Thanks for the work on this, LGTM, so ack. Thanks, Tao Liu On Fri, May 29, 2026 at 5:00 PM HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab(a)nec.com&gt; wrote: > > From: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; > > On x86_64, the "bt" command resolves saved return addresses with > value_search(textaddr). However, a return address is the instruction > pointer after the call, not the call site itself. > > This becomes a problem when the caller ends with a call to a noreturn > function. In that case, the saved return address can match the start > address of the following symbol, and "bt" loses track of the call chain > and this can lead to very long session initialization. > > The same issue also affects symbol+offset formatting, line number > lookup, and ORC-based frame size resolution. > > Fix it by resolving normal backtrace return addresses with textaddr-1, > while keeping exact textaddr handling for real RIP values saved in > exception frames. Add value_to_symstr_trace() so the displayed > symbol+offset still reflects the original return address value. > > Suggested-by: Kosuke Tatsukawa <tatsu-ab1(a)nec.com&gt; > Signed-off-by: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; > --- > defs.h | 1 + > symbols.c | 24 +++++++++++++++++++++--- > x86_64.c | 31 ++++++++++++++++++++++++++----- > 3 files changed, 48 insertions(+), 8 deletions(-) > > diff --git a/defs.h b/defs.h > index 89044b18cdbe..79969df2a8c2 100644 > --- a/defs.h > +++ b/defs.h > @@ -5798,6 +5798,7 @@ struct syment *prev_symbol(char *, struct syment *); > void get_symbol_data(char *, long, void *); > int try_get_symbol_data(char *, long, void *); > char *value_to_symstr(ulong, char *, ulong); > +char *value_to_symstr_trace(ulong, char *, ulong); > char *value_symbol(ulong); > ulong symbol_value(char *); > ulong symbol_value_module(char *, char *); > diff --git a/symbols.c b/symbols.c > index 3c62f54d4a93..372d0b230b18 100644 > --- a/symbols.c > +++ b/symbols.c > @@ -104,6 +104,7 @@ static void free_structure(struct struct_elem *); > static unsigned char is_right_brace(const char *); > static struct struct_elem *find_node(struct struct_elem *, char *); > static void dump_node(struct struct_elem *, char *, unsigned char, unsigned char); > +static char *_value_to_symstr(ulong value, char *buf, ulong radix, int trace); > > static int module_mem_type(ulong, struct load_module *); > static ulong module_mem_end(ulong, struct load_module *); > @@ -5973,14 +5974,25 @@ generic_machdep_value_to_symbol(ulong value, ulong *offset) > return NULL; > } > > +char * > +value_to_symstr(ulong value, char *buf, ulong radix) > +{ > + return _value_to_symstr(value, buf, radix, 0); > +} > + > +char * > +value_to_symstr_trace(ulong value, char *buf, ulong radix) > +{ > + return _value_to_symstr(value, buf, radix, 1); > +} > > /* > * For a given value, format a string containing the nearest symbol name > * plus the offset if appropriate. Display the offset in the specified > * radix (10 or 16) -- if it's 0, set it to the current pc->output_radix. > */ > -char * > -value_to_symstr(ulong value, char *buf, ulong radix) > +static char * > +_value_to_symstr(ulong value, char *buf, ulong radix, int trace) > { > struct syment *sp; > ulong offset; > @@ -5996,7 +6008,13 @@ value_to_symstr(ulong value, char *buf, ulong radix) > if ((radix != 10) && (radix != 16)) > radix = 16; > > - if ((sp = value_search(value, &offset))) { > + if (trace) { > + sp = value_search(value-1, &offset); > + offset++; > + } else > + sp = value_search(value, &offset); > + > + if (sp) { > if (offset) > sprintf(buf, radix == 16 ? "%s+0x%lx" : "%s+%ld", > sp->name, offset); > diff --git a/x86_64.c b/x86_64.c > index b2cddbf8ba3d..ff283ed68191 100644 > --- a/x86_64.c > +++ b/x86_64.c > @@ -3229,14 +3229,23 @@ x86_64_print_stack_entry(struct bt_info *bt, FILE *ofp, int level, > if (!(bt->flags & BT_SAVE_EFRAME_IP)) > bt->eframe_ip = 0; > offset = 0; > - sp = value_search(text, &offset); > + if (bt->flags & BT_SAVE_EFRAME_IP) > + sp = value_search(text, &offset); > + else { > + sp = value_search(text-1, &offset); > + offset++; > + } > if (!sp) > return BACKTRACE_ENTRY_IGNORED; > > name = sp->name; > > if (offset && (bt->flags & BT_SYMBOL_OFFSET)) > - name_plus_offset = value_to_symstr(text, buf2, bt->radix); > + if (bt->flags & BT_SAVE_EFRAME_IP) > + name_plus_offset = value_to_symstr(text, buf2, bt->radix); > + else > + /* text-1 is used in the function */ > + name_plus_offset = value_to_symstr_trace(text, buf2, bt->radix); > else > name_plus_offset = NULL; > > @@ -3337,7 +3346,10 @@ x86_64_print_stack_entry(struct bt_info *bt, FILE *ofp, int level, > fprintf(ofp, "\n"); > > if (bt->flags & BT_LINE_NUMBERS) { > - get_line_number(text, buf1, FALSE); > + if (bt->flags & BT_SAVE_EFRAME_IP) > + get_line_number(text, buf1, FALSE); > + else > + get_line_number(text-1, buf1, FALSE); > if (strlen(buf1)) > fprintf(ofp, " %s\n", buf1); > } > @@ -3864,8 +3876,10 @@ in_exception_stack: > } > > level++; > + bt->flags |= BT_SAVE_EFRAME_IP; > if ((framesize = x86_64_get_framesize(bt, bt->instptr, rsp, NULL)) >= 0) > rsp += framesize; > + bt->flags &= ~BT_SAVE_EFRAME_IP; > } > } > > @@ -8811,7 +8825,13 @@ x86_64_get_framesize(struct bt_info *bt, ulong textaddr, ulong rsp, char *stack_ > return 0; > } > > - if (!(sp = value_search(textaddr, &offset))) { > + if (bt->flags & BT_SAVE_EFRAME_IP) > + sp = value_search(textaddr, &offset); > + else { > + sp = value_search(textaddr-1, &offset); > + offset++; > + } > + if (!sp) { > if (!(bt->flags & BT_FRAMESIZE_DEBUG)) > bt->flags |= BT_FRAMESIZE_DISABLE; > return 0; > @@ -8887,7 +8907,8 @@ x86_64_get_framesize(struct bt_info *bt, ulong textaddr, ulong rsp, char *stack_ > if ((sp->value >= kt->init_begin) && (sp->value < kt->init_end)) > return 0; > > - if ((machdep->flags & ORC) && (korc = orc_find(textaddr))) { > + if ((machdep->flags & ORC) && > + (korc = orc_find(bt->flags & BT_SAVE_EFRAME_IP ? textaddr : textaddr-1))) { > if (CRASHDEBUG(1)) { > struct ORC_data *orc = &machdep->machspec->orc; > fprintf(fp, > -- > 2.31.1 >