Messages in this thread | | | Date | Fri, 31 May 2019 10:27:28 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] Stacktrace in ARM32 architecture has jumped the first 2 layers, which may ignore the display of save_stack_trace_tsk. |
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On Thu, May 30, 2019 at 05:22:19PM +0100, Russell King - ARM Linux admin wrote: > On Thu, May 30, 2019 at 11:06:39PM +0800, l00383200 wrote: > > Without optimization, both save_stack_trace_tsk and __save_stack_trace > > will have stacktrace information in ARM32. > > > > In this situation, "data.skip += 2" operation will skip the first two layers, > > which may make the stacktrace strange and different from other architectures. > > > > A simple example is as follows: > > In ARM32 architecture: > > [<ffffff80083cb3f8>] proc_pid_stack+0xac/0x12c > > [<ffffff80083c7c70>] proc_single_show+0x5c/0xa8 > > [<ffffff800838aca8>] seq_read+0x130/0x420 > > [<ffffff8008365c54>] __vfs_read+0x60/0x11c > > [<ffffff80083665dc>] vfs_read+0x8c/0x140 > > [<ffffff800836717c>] SyS_read+0x6c/0xcc > > [<ffffff8008202cb8>] __sys_trace_return+0x0/0x4 > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > In some other architectures(ARM64): > > [<ffffff8008209be0>] save_stack_trace_tsk+0x0/0xf0 > > [<ffffff80083cb3f8>] proc_pid_stack+0xac/0x12c > > [<ffffff80083c7c70>] proc_single_show+0x5c/0xa8 > > [<ffffff800838aca8>] seq_read+0x130/0x420 > > [<ffffff8008365c54>] __vfs_read+0x60/0x11c > > [<ffffff80083665dc>] vfs_read+0x8c/0x140 > > [<ffffff800836717c>] SyS_read+0x6c/0xcc > > [<ffffff8008202cb8>] __sys_trace_return+0x0/0x4 > > [<ffffffffffffffff>] 0xffffffffffffffff > > > > Therefore, we'd better just jump only one layer to ensure accuracy and consistency. > > Why do we want to log the function we called to save the stack trace > _in_ the stack trace? What useful purpose does it serve? > > I've always taken the attitude that if we want a stack trace from a > certain point in the function, then that's the point that the stack > trace should start. It's entirely sensible.
Agreed, also the .skip interface sucks and is slated for replacement (whenever we get around to it).
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