From 450ec38d793a0f85d3afb6d6c2e9d59d8b607fd9 Mon Sep 17 00:00:00 2001 From: Daniel Stone Date: Sat, 25 Jun 2022 16:38:35 +0100 Subject: [PATCH] noop-renderer: Make sure buffer access doesn't get optimised out noop-renderer needs to actually access the buffer content, to ensure that the bad-buffer test works. This was previously done using a volatile variable, but clang rightly pointed out that the variable access had no effect (since the volatile stack variable was never read from, and the source is not volatile), so 9b0b5b57ddca changed it to be explicitly marked it as unused to suppress the compiler warning. Unfortunately suppressing the warning still leaves the compiler free to optimise out the access. Replace the variable decorations with actually using the result of the read, so we can be really sure that it's never going to be optimised away. Signed-off-by: Daniel Stone --- libweston/noop-renderer.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/libweston/noop-renderer.c b/libweston/noop-renderer.c index e6ab8ee4..731d1371 100644 --- a/libweston/noop-renderer.c +++ b/libweston/noop-renderer.c @@ -31,6 +31,11 @@ #include #include "libweston-internal.h" +struct noop_renderer { + struct weston_renderer base; + unsigned char seed; /* see comment in attach() */ +}; + static int noop_renderer_read_pixels(struct weston_output *output, pixman_format_code_t format, void *pixels, @@ -55,10 +60,12 @@ noop_renderer_flush_damage(struct weston_surface *surface, static void noop_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer) { + struct noop_renderer *renderer = + wl_container_of(es->compositor->renderer, renderer, base); struct wl_shm_buffer *shm_buffer; uint8_t *data; uint32_t size, i, height, stride; - __attribute__((unused)) int unused = 0; + unsigned char unused = 0; if (!buffer) return; @@ -90,11 +97,18 @@ noop_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer) unused ^= data[i]; wl_shm_buffer_end_access(shm_buffer); + /* Make sure that our unused is actually used, otherwise the compiler + * is free to notice that our reads have no effect and elide them. */ + renderer->seed = unused; } static void noop_renderer_destroy(struct weston_compositor *ec) { + struct noop_renderer *renderer = + wl_container_of(ec->renderer, renderer, base); + + weston_log("no-op renderer SHM seed: %d\n", renderer->seed); free(ec->renderer); ec->renderer = NULL; } @@ -102,18 +116,18 @@ noop_renderer_destroy(struct weston_compositor *ec) WL_EXPORT int noop_renderer_init(struct weston_compositor *ec) { - struct weston_renderer *renderer; + struct noop_renderer *renderer; renderer = zalloc(sizeof *renderer); if (renderer == NULL) return -1; - renderer->read_pixels = noop_renderer_read_pixels; - renderer->repaint_output = noop_renderer_repaint_output; - renderer->flush_damage = noop_renderer_flush_damage; - renderer->attach = noop_renderer_attach; - renderer->destroy = noop_renderer_destroy; - ec->renderer = renderer; + renderer->base.read_pixels = noop_renderer_read_pixels; + renderer->base.repaint_output = noop_renderer_repaint_output; + renderer->base.flush_damage = noop_renderer_flush_damage; + renderer->base.attach = noop_renderer_attach; + renderer->base.destroy = noop_renderer_destroy; + ec->renderer = &renderer->base; return 0; }