RE: [PATCH 1/1] get page size using sysconf (_SC_PAGESIZE) instead of PAGE_SIZE

["Metzger, Markus T via Gdb-patches" <gdb-patches@sourceware.org>]

Hello Zied,

>diff --git a/gdb/nat/linux-btrace.c b/gdb/nat/linux-btrace.c
>index b0d6dcd7cf1..a9aaa9c88b3 100644
>--- a/gdb/nat/linux-btrace.c
>+++ b/gdb/nat/linux-btrace.c
>@@ -486,9 +486,10 @@ linux_enable_bts (ptid_t ptid, const struct
>btrace_config_bts *conf)
>   if (fd.get () < 0)
>     diagnose_perf_event_open_fail ();
>
>+  long page_size = sysconf (_SC_PAGESIZE);

Please check the return value.  You may just error out but we should
detect errors, at least.


>   struct perf_event_mmap_page *header = (struct perf_event_mmap_page *)
>     data.get ();
>-  data_offset = PAGE_SIZE;
>+  data_offset = page_size;

Hmmm, I would have expected a compiler warning, here, since PAGE_SIZE is
now long and DATA_OFFSET is __u64.


>   /* Allocate the configuration page. */
>-  scoped_mmap data (nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE,
>MAP_SHARED,
>+  long page_size = sysconf (_SC_PAGESIZE);

Here, we'd also want to check the return value.


>@@ -661,7 +663,7 @@ linux_enable_pt (ptid_t ptid, const struct
>btrace_config_pt *conf)
>       size_t length;
>       __u64 data_size;
>
>-      data_size = (__u64) pages * PAGE_SIZE;
>+      data_size = (__u64) pages * page_size;

Hmmm, this also looks like the compiler would want to warn about
signed and unsigned multiply.

Regards,
Markus.

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