Re: [PATCH] powerpc: Fix kernel-jump address for ppc64 wrapper boot

[Christophe Leroy]

Le 04/06/2021 à 11:22, He Ying a écrit :
 From "64-bit PowerPC ELF Application Binary Interface Supplement 1.9",
we know that the value of a function pointer in a language like C is
the address of the function descriptor and the first doubleword
of the function descriptor contains the address of the entry point
of the function.

So, when we want to jump to an address (e.g. addr) to execute for
PPC-elf64abi, we should assign the address of addr *NOT* addr itself
to the function pointer or system will jump to the wrong address.

Link: https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#FUNC-DES
Signed-off-by: He Ying <heyin...@huawei.com>
---
  arch/powerpc/boot/main.c | 9 +++++++++
  1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/boot/main.c b/arch/powerpc/boot/main.c
index cae31a6e8f02..50fd7f11b642 100644
--- a/arch/powerpc/boot/main.c
+++ b/arch/powerpc/boot/main.c
@@ -268,7 +268,16 @@ void start(void)
        if (console_ops.close)
                console_ops.close();
  
+#ifdef CONFIG_PPC64_BOOT_WRAPPER

This kind of need doesn't desserve a #ifdef, see 
https://www.kernel.org/doc/html/latest/process/coding-style.html#conditional-compilation

You can do:


        kentry = (kernel_entry_t)(IS_ENABLED(CONFIG_PPC64_BOOT_WRAPPER) ? 
&vmlinux.addr : vmlinux.addr);


Or, if you prefer something less compact:


        if (IS_ENABLED(CONFIG_PPC64_BOOT_WRAPPER))
                kentry = (kernel_entry_t) &vmlinux.addr;
        else
                kentry = (kernel_entry_t) vmlinux.addr;


+       /*
+        * For PPC-elf64abi, the value of a function pointer is the address
+        * of the function descriptor. And the first doubleword of a function
+        * descriptor contains the address of the entry point of the function.
+        */
+       kentry = (kernel_entry_t) &vmlinux.addr;
+#else
        kentry = (kernel_entry_t) vmlinux.addr;
+#endif
        if (ft_addr) {
                if(platform_ops.kentry)
                        platform_ops.kentry(ft_addr, vmlinux.addr);