Re: [PATCH] RISC-V: Handle R_RISCV_32 in modules

From: Palmer Dabbelt
Date: Mon Jun 11 2018 - 16:53:36 EST


On Mon, 11 Jun 2018 00:54:00 PDT (-0700), schwab@xxxxxxx wrote:
On Jun 08 2018, Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:

On Thu, 07 Jun 2018 03:27:27 PDT (-0700), schwab@xxxxxxx wrote:
With CONFIG_MODVERSIONS=y the R_RISCV_32 relocation is used by the
__kcrctab section.

Signed-off-by: Andreas Schwab <schwab@xxxxxxx>
---
arch/riscv/kernel/module.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 5dddba301d..1d5e9b934b 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -17,6 +17,17 @@
#include <linux/errno.h>
#include <linux/moduleloader.h>

+static int apply_r_riscv_32_rela(struct module *me, u32 *location, Elf_Addr v)
+{
+ if (v != (u32)v) {

My worry with this kind of check is that it relies on some sort of
undefined behavior in C and that at some point in the future GCC will just
go decide the check can never fail. I checked and GCC doesn't elide these
checks now, so I might be wrong.

Is this defined to do what it looks like it's doing?

This is unsigned arithmetic, thus fully defined.

Great, thanks! I guess I'm just a bit paranoid :)