diff options
Diffstat (limited to 'doc/il.txt')
| -rw-r--r-- | doc/il.txt | 65 |
1 files changed, 53 insertions, 12 deletions
diff --git a/doc/il.txt b/doc/il.txt index 2236340..b667b64 100644 --- a/doc/il.txt +++ b/doc/il.txt @@ -15,14 +15,15 @@ * <@ Simple Types > * <@ Subtyping > 3. <@ Constants > - 4. <@ Definitions > + 4. <@ Linkage > + 5. <@ Definitions > * <@ Aggregate Types > * <@ Data > * <@ Functions > - 5. <@ Control > + 6. <@ Control > * <@ Blocks > * <@ Jumps > - 6. <@ Instructions > + 7. <@ Instructions > * <@ Arithmetic and Bits > * <@ Memory > * <@ Comparisons > @@ -31,7 +32,7 @@ * <@ Call > * <@ Variadic > * <@ Phi > - 7. <@ Instructions Index > + 8. <@ Instructions Index > - 1. Basic Concepts ------------------- @@ -196,7 +197,46 @@ Global symbols can also be used directly as constants; they will be resolved and turned into actual numeric constants by the linker. -- 4. Definitions +- 4. Linkage +------------ + + `bnf + LINKAGE := + 'extern' + | 'section' SECNAME + | 'section' SECNAME SECFLAGS + + SECNAME := '"' .... '"' + SECFLAGS := '"' .... '"' + +Function and data definitions (see below) can specify +linkage information to be passed to the assembler and +eventually to the linker. + +The `extern` linkage flag marks the defined item as +visible outside the current file's scope. If absent, +the symbol can only be referred to locally. Functions +compiled by QBE and called from C need to have extern +linkage. + +A `section` flag can be specified to tell the linker to +put the defined item in a certain section. The use of +the section flag is platform dependent and we refer the +user to the documentation of their assembler and linker +for relevant information. + + export section ".bss" + data $zerobuf = { z 1024 } + +Example uses of the section flag include adding function +pointers to a global initialization list, or storing a +zeroed object in the BSS section, as depicted above. + +The section and extern linkage flags should each appear +at most once in a definition. If multiple occurrences +are present, QBE is free to use any. + +- 5. Definitions ---------------- Definitions are the essential components of an IL file. @@ -254,7 +294,7 @@ their size between curly braces. `bnf DATADEF := - ['export'] 'data' $IDENT '=' ['align' NUMBER] + LINKAGE* 'data' $IDENT '=' ['align' NUMBER] '{' ( EXTTY DATAITEM+ | 'z' NUMBER ), @@ -266,8 +306,9 @@ their size between curly braces. | CONST # Constant Data definitions express objects that will be emitted in the -compiled file. They can be local to the file or exported -with global visibility to the whole program. +compiled file. Their visibility and location in the compiled +artifact are controlled with linkage flags described in the +<@ Linkage > section. They define a global identifier (starting with the sigil `$`), that will contain a pointer to the object specified @@ -311,7 +352,7 @@ Here are various examples of data definitions. `bnf FUNCDEF := - ['export'] 'function' [ABITY] $IDENT '(' (PARAM), ')' + LINKAGE* 'function' [ABITY] $IDENT '(' (PARAM), ')' '{' BLOCK+ '}' @@ -384,7 +425,7 @@ is provided in the call instructions. The syntax and semantics for the body of functions are described in the <@ Control > section. -- 5. Control +- 6. Control ------------ The IL represents programs as textual transcriptions of @@ -465,7 +506,7 @@ the following list. prototype. If the function prototype does not specify a return type, no return value can be used. -- 6. Instructions +- 7. Instructions ----------------- Instructions are the smallest piece of code in the IL, they @@ -903,7 +944,7 @@ assumes that if a variable is defined by a phi it respects all the SSA invariants. So it is critical to not use phi instructions unless you know exactly what you are doing. -- 7. Instructions Index +- 8. Instructions Index ----------------------- * <@ Arithmetic and Bits >: |