Changeset a35a3d8 in mainline for uspace/lib/c/arch/amd64/src/fibril.S

Timestamp:

2018-03-12T17:13:46Z (6 years ago)

Author:

GitHub <noreply@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

b127e4af

Parents:

f3d47c97

git-author:

Jiří Zárevúcky <zarevucky.jiri@…> (2018-03-12 17:13:46)

git-committer:

GitHub <noreply@…> (2018-03-12 17:13:46)

Message:

Turn context_save/context_restore into standard setjmp/longjmp. (#24)

Turn context_save()/context_restore() into semi-standard __setjmp()/__longjmp().

The original context_* functions are similar to setjmp()/longjmp(), except that the return value is more restricted for the former, and with inverted meaning. This commit adopts the standard return value semantics and acknowledges that these functions are "standard setjmp()/longjmp() with additional implementation-specific properties" by changing the name. The only divergence from the standard is that __longjmp() causes __setjmp() to return its value unchanged, even if it is zero. This is just to avoid extra assembly, and longjmp() checks this in C.

Note that the original use of context_save()/context_restore() to implement context switching in fibril implementation has already been delegated to context_create()/context_swap(), which provide more natural control flow.

File:

• uspace/lib/c/arch/amd64/src/fibril.S (modified) (3 diffs)

uspace/lib/c/arch/amd64/src/fibril.S

@@ -35 +35 @@
 #
 # Save CPU context to context_t variable
-# pointed by the 1st argument. Returns 1 in EAX.
+# pointed by the 1st argument. Returns 0 in RAX.
 #
-FUNCTION_BEGIN(context_save)
+FUNCTION_BEGIN(__setjmp)
         movq (%rsp), %rdx     # the caller's return %eip
 
@@ -54 +54 @@
         movq %rax, CONTEXT_OFFSET_TLS(%rdi)
 
-        xorl %eax, %eax                      # context_save returns 1
-        incl %eax
+        xorq %rax, %rax                      # __setjmp returns 0
         ret
-FUNCTION_END(context_save)
+FUNCTION_END(__setjmp)
 
 ## Restore current CPU context
 #
 # Restore CPU context from context_t variable
-# pointed by the 1st argument. Returns 0 in EAX.
+# pointed by the 1st argument. Returns second argument in RAX.
 #
-FUNCTION_BEGIN(context_restore)
+FUNCTION_BEGIN(__longjmp)
         movq CONTEXT_OFFSET_R15(%rdi), %r15
         movq CONTEXT_OFFSET_R14(%rdi), %r14
@@ -81 +80 @@
         movq %rdi, %fs:0
 
-        xorl %eax, %eax                      # context_restore returns 0
+        movq %rsi, %rax                      # __longjmp returns second argument
         ret
-FUNCTION_END(context_restore)
+FUNCTION_END(__longjmp)