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powerpc/bpf/32: Only set a stack frame when necessary 

Until now a stack frame was set at all time due to the need
to keep tail call counter in the stack.

But since commit 89d21e259a ("powerpc/bpf/32: Fix Oops on tail call
tests") the tail call counter is passed via register r4. It is therefore
not necessary anymore to have a stack frame for that.

Just like PPC64, implement bpf_has_stack_frame() and only sets the frame
when needed.

The difference with PPC64 is that PPC32 doesn't have a redzone, so
the stack is required as soon as non volatile registers are used or
when tail call count is set up.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix commit reference in change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/62d7b654a3cfe73d998697cb29bbc5ffd89bfdb1.1675245773.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2023-02-01 11:04:25 +01:00 committed by Michael Ellerman
parent 6376ed8fec
commit d084dcf256
1 changed files with 18 additions and 2 deletions
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20
arch/powerpc/net/bpf_jit_comp32.c
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@ -79,6 +79,20 @@ static int bpf_jit_stack_offsetof(struct codegen_context *ctx, int reg)
#define SEEN_NVREG_FULL_MASK 0x0003ffff /* Non volatile registers r14-r31 */
#define SEEN_NVREG_TEMP_MASK 0x00001e01 /* BPF_REG_5, BPF_REG_AX, TMP_REG */
static inline bool bpf_has_stack_frame(struct codegen_context *ctx)
{
/*
* We only need a stack frame if:
* - we call other functions (kernel helpers), or
* - we use non volatile registers, or
* - we use tail call counter
* - the bpf program uses its stack area
* The latter condition is deduced from the usage of BPF_REG_FP
*/
return ctx->seen & (SEEN_FUNC | SEEN_TAILCALL | SEEN_NVREG_FULL_MASK) ||
bpf_is_seen_register(ctx, bpf_to_ppc(BPF_REG_FP));
}
void bpf_jit_realloc_regs(struct codegen_context *ctx)
{
unsigned int nvreg_mask;
@ -121,7 +135,8 @@ void bpf_jit_build_prologue(u32 *image, struct codegen_context *ctx)
#define BPF_TAILCALL_PROLOGUE_SIZE 4
EMIT(PPC_RAW_STWU(_R1, _R1, -BPF_PPC_STACKFRAME(ctx)));
if (bpf_has_stack_frame(ctx))
EMIT(PPC_RAW_STWU(_R1, _R1, -BPF_PPC_STACKFRAME(ctx)));
if (ctx->seen & SEEN_TAILCALL)
EMIT(PPC_RAW_STW(_R4, _R1, bpf_jit_stack_offsetof(ctx, BPF_PPC_TC)));
@ -174,7 +189,8 @@ static void bpf_jit_emit_common_epilogue(u32 *image, struct codegen_context *ctx
EMIT(PPC_RAW_LWZ(_R0, _R1, BPF_PPC_STACKFRAME(ctx) + PPC_LR_STKOFF));
/* Tear down our stack frame */
EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME(ctx)));
if (bpf_has_stack_frame(ctx))
EMIT(PPC_RAW_ADDI(_R1, _R1, BPF_PPC_STACKFRAME(ctx)));
if (ctx->seen & SEEN_FUNC)
EMIT(PPC_RAW_MTLR(_R0));