[Crash-utility] Re: [PATCH] Fix dis -lr xxx+0x1 not showing target address instruction

On Sat, Feb 14, 2026 at 8:43 PM Lianbo Jiang <lijiang(a)redhat.com&gt; wrote: > > On 1/28/26 9:42 AM, devel-request(a)lists.crash-utility.osci.io wrote: > > > Date: Mon, 15 Dec 2025 17:15:15 +0800 > > From: neilfsun&lt;loyou85(a)gmail.com&gt; > > Subject: [Crash-utility] [PATCH] Fix dis -lr xxx+0x1 not showing > > target address instruction > > To:devel@lists.crash-utility.osci.io > > Cc: neilfsun&lt;neilfsun(a)tencent.com&gt;, Feng Sun&lt;loyou85(a)gmail.com&gt; > > Message-ID:<20251215091515.36428-1-neilfsun@tencent.com> > > > > When using "dis -lr xxx+0x1", it is not correctly shown, for example: > > crash> dis -lr rb_next+0x1 > > /kernel/lib/rbtree.c: 445 > > 0xffffffff8133ff60 <rb_next>: push %rbp > > > > However, dis -lr rb+next+0x4 is correctly shown, > > crash> dis -lr rb_next+0x4 > > /kernel/lib/rbtree.c: 445 > > 0xffffffff8133ff60 <rb_next>: push %rbp > > /kernel/lib/rbtree.c: 448 > > 0xffffffff8133ff61 <rb_next+0x1>: mov (%rdi),%rdx > > /kernel/lib/rbtree.c: 445 > > 0xffffffff8133ff64 <rb_next+0x4>: mov %rsp,%rbp > > > > The reverse mode only disassembled (target - function_start) bytes, which > > was insufficient to reach the target instruction. > > > > Signed-off-by: neilfsun&lt;neilfsun(a)tencent.com&gt; > > Signed-off-by: Feng Sun&lt;loyou85(a)gmail.com&gt; > > --- > > kernel.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel.c b/kernel.c > > index bb148d0..93ea7a6 100644 > > --- a/kernel.c > > +++ b/kernel.c > > @@ -2120,7 +2120,7 @@ cmd_dis(void) > > > > if (reverse) > > sprintf(buf5, "x/%ldi 0x%lx", > > - (target - req->addr) ? target - req->addr : 1, > > + req->addr2 - req->addr, > > This will always ask gdb to disassemble a lot of asm instructions, can Indeed. We will disassemble all instructions of the function, but only take the first few instructions for output, that would be a waste. > you help try this one? > > diff --git a/kernel.c b/kernel.c > index ccc4b3d..550f61a 100644 > --- a/kernel.c > +++ b/kernel.c > @@ -2124,8 +2124,7 @@ cmd_dis(void) > open_tmpfile(); > > if (reverse) > - sprintf(buf5, "x/%ldi 0x%lx", > - (target - req->addr) ? target - > req->addr : 1, > + sprintf(buf5, "x/%ldi 0x%lx", roundup(abs(target > - req->addr), 2), This one also have some problems: crash> dis -r rb_next+0 <<----should output 1 instruction to include "rb_next+0" crash> dis -r rb_next+1 <<---- OK 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx crash> dis -r rb_next+2 <<---- should output 3 instruction, because "rb_next+2" is not included by any outputted instructions. 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx crash> dis -r rb_next+3 <<---- OK 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp crash> dis -r rb_next+4 <<---- OK 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp crash> dis -r rb_next+5 <<---- OK 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp 0xffffffff81329607 <rb_next+7>: cmp %rdx,%rdi In addition, the 2 in roundup() is a magic number to me. Good findings, Tao.

How about the following modification: if (reverse) sprintf(buf5, "x/%ldi 0x%lx", - (target - req->addr) ? target - req->addr : 1, + abs(target - req->addr) + 1, req->addr);

0xffffffff81329600 <rb_next>: push %rbp crash> dis -r rb_next+1 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx crash> dis -r rb_next+2 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp crash> dis -r rb_next+3 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp crash> dis -r rb_next+4 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp crash> dis -r rb_next+5 0xffffffff81329600 <rb_next>: push %rbp 0xffffffff81329601 <rb_next+1>: mov (%rdi),%rdx 0xffffffff81329604 <rb_next+4>: mov %rsp,%rbp 0xffffffff81329607 <rb_next+7>: cmp %rdx,%rdi Thanks, Tao Liu > req->addr); > else > sprintf(buf5, "x/%ldi 0x%lx", > > Thanks > > Lianbo > > > req->addr); > > else > > sprintf(buf5, "x/%ldi 0x%lx", > > -- 2.50.1 > -- > Crash-utility mailing list -- devel(a)lists.crash-utility.osci.io > To unsubscribe send an email to devel-leave(a)lists.crash-utility.osci.io > https://${domain_name}/admin/lists/devel.lists.crash-utility.osci.io/ > Contribution Guidelines: https://github.com/crash-utility/crash/wiki