Add large code model information.

Author: Kuan-Lin Chen

riscv-elf.adoc

@@ -125,6 +125,41 @@ This model is similar to the medium any code model, but uses the
          l[w|d] a0, a0, %pcrel_lo(.Ltmp3)
 ----
 
+=== Large code model
+
+The `large` code model allows the code to address the whole RV64 address space.
+Thus, this model is only available for RV64. By putting object addresses
+into literal pools, a 64-bit address literal can be loaded from the pool.
+This model also changes the function call patterns. An external function
+address must be loaded from a literal pool entry, and use `jalr` to jump to
+the target function.
+
+NOTE: Because calculating the pool entry address must use `aupic` and
+`addi` or `ld`, each pool entry has to be located within the range
+between -2GiB and +2GiB from its access intructions.  In general, the pool
+is appeneded in .text section or put into .rodata section.
+
+NOTE: Large code model is disallowed using with PIC code model.
+
+[,asm]
+----
+         # Get address of a symbol
+         # Literal pool
+         .LCPI0:
+           .dword symbol
+.Ltmp0:  auipc   a0, %pcrel_hi(.LCPI0)
+         ld      a0, %pcrel_lo(.Ltmp0)(10)
+
+         # Function call
+         # Literal pool
+         .LCPI1:
+           .dword function
+.Ltmp1:  auipc   a0, %pcrel_hi(.LCPI1)
+         ld      a0, %pcrel_lo(.Ltmp1)(a0)
+         jalr    a0
+
+----
+
 == Dynamic Linking
 
 Any functions that use registers in a way that is incompatible with