[U-Boot] [PATCH v4 05/16] sandbox: Add a setjmp() implementation

[Alexander Graf]

On 16.05.18 17:42, Simon Glass wrote:
> Add an implementation of setjmp() and longjmp() which rely on the
> underlying host C library. Since we cannot know how large the jump buffer
> needs to be, pick something that should be suitable and check it at
> runtime. At present we need access to the underlying struct as well.
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
> 
> Changes in v4:
> - Fix up the sizeof() operations on jmp_buf
> - Update SPDX tags
> 
> Changes in v3: None
> Changes in v2: None
> 
>  arch/sandbox/cpu/cpu.c            | 13 +++++++++++++
>  arch/sandbox/cpu/os.c             | 23 +++++++++++++++++++++++
>  arch/sandbox/include/asm/setjmp.h | 30 ++++++++++++++++++++++++++++++
>  include/os.h                      | 21 +++++++++++++++++++++
>  4 files changed, 87 insertions(+)
>  create mode 100644 arch/sandbox/include/asm/setjmp.h
> 
> diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
> index d4ad020012e..cde0b055a67 100644
> --- a/arch/sandbox/cpu/cpu.c
> +++ b/arch/sandbox/cpu/cpu.c
> @@ -9,6 +9,7 @@
>  #include <linux/libfdt.h>
>  #include <os.h>
>  #include <asm/io.h>
> +#include <asm/setjmp.h>
>  #include <asm/state.h>
>  #include <dm/root.h>
>  
> @@ -164,3 +165,15 @@ ulong timer_get_boot_us(void)
>  
>  	return (count - base_count) / 1000;
>  }
> +
> +int setjmp(jmp_buf jmp)
> +{
> +	return os_setjmp((ulong *)jmp, sizeof(*jmp));

So, this doesn't work. Function returns increase the stack pointer which
means after setjmp() you are not allowed to return until the longjmp
occured. The documentation is quite clear about this:


DESCRIPTION
       setjmp() and longjmp(3) are useful for dealing with errors and
interrupts encountered in a low-level subroutine of a program.  setjmp()
saves the stack context/environment in env for later use by longjmp(3).
The stack context will be invalidated if the function which called
setjmp() returns.


So we need to find a way to call setjmp() directly from the code point
where we want to call it, rather than jump through helper functions, as
these break its functionality.

Also, os_longjmp() is broken. It calls longjmp() which however is not
the system longjmp, but the U-Boot internal one that again calls
os_longjmp. My quick fix was to make it call _longjmp() instead - that
at least makes that part work.


Alex