Using as: Sparc-Relocs

Using as: Sparc-Relocs

9.44.3.4 Relocations

ELF relocations are available as defined in the 32-bit and 64-bit Sparc ELF specifications.

R_SPARC_HI22 is obtained using ‘%hi’ and R_SPARC_LO10 is obtained using ‘%lo’. Likewise R_SPARC_HIX22 is obtained from ‘%hix’ and R_SPARC_LOX10 is obtained using ‘%lox’. For example:

sethi %hi(symbol), %g1
or    %g1, %lo(symbol), %g1
sethi %hix(symbol), %g1
xor   %g1, %lox(symbol), %g1

These “high” mnemonics extract bits 31:10 of their operand, and the “low” mnemonics extract bits 9:0 of their operand.

V9 code model relocations can be requested as follows:

R_SPARC_HH22 is requested using ‘%hh’. It can also be generated using ‘%uhi’.
R_SPARC_HM10 is requested using ‘%hm’. It can also be generated using ‘%ulo’.
R_SPARC_LM22 is requested using ‘%lm’.
R_SPARC_H44 is requested using ‘%h44’.
R_SPARC_M44 is requested using ‘%m44’.
R_SPARC_L44 is requested using ‘%l44’ or ‘%l34’.
R_SPARC_H34 is requested using ‘%h34’.

The ‘%l34’ generates a R_SPARC_L44 relocation because it calculates the necessary value, and therefore no explicit R_SPARC_L34 relocation needed to be created for this purpose.

The ‘%h34’ and ‘%l34’ relocations are used for the abs34 code model. Here is an example abs34 address generation sequence:

sethi %h34(symbol), %g1
sllx  %g1, 2, %g1
or    %g1, %l34(symbol), %g1

The PC relative relocation R_SPARC_PC22 can be obtained by enclosing an operand inside of ‘%pc22’. Likewise, the R_SPARC_PC10 relocation can be obtained using ‘%pc10’. These are mostly used when assembling PIC code. For example, the standard PIC sequence on Sparc to get the base of the global offset table, PC relative, into a register, can be performed as:

sethi %pc22(_GLOBAL_OFFSET_TABLE_-4), %l7
add   %l7, %pc10(_GLOBAL_OFFSET_TABLE_+4), %l7

Several relocations exist to allow the link editor to potentially optimize GOT data references. The R_SPARC_GOTDATA_OP_HIX22 relocation can obtained by enclosing an operand inside of ‘%gdop_hix22’. The R_SPARC_GOTDATA_OP_LOX10 relocation can obtained by enclosing an operand inside of ‘%gdop_lox10’. Likewise, R_SPARC_GOTDATA_OP can be obtained by enclosing an operand inside of ‘%gdop’. For example, assuming the GOT base is in register %l7:

sethi %gdop_hix22(symbol), %l1
xor   %l1, %gdop_lox10(symbol), %l1
ld    [%l7 + %l1], %l2, %gdop(symbol)

There are many relocations that can be requested for access to thread local storage variables. All of the Sparc TLS mnemonics are supported:

R_SPARC_TLS_GD_HI22 is requested using ‘%tgd_hi22’.
R_SPARC_TLS_GD_LO10 is requested using ‘%tgd_lo10’.
R_SPARC_TLS_GD_ADD is requested using ‘%tgd_add’.
R_SPARC_TLS_GD_CALL is requested using ‘%tgd_call’.
R_SPARC_TLS_LDM_HI22 is requested using ‘%tldm_hi22’.
R_SPARC_TLS_LDM_LO10 is requested using ‘%tldm_lo10’.
R_SPARC_TLS_LDM_ADD is requested using ‘%tldm_add’.
R_SPARC_TLS_LDM_CALL is requested using ‘%tldm_call’.
R_SPARC_TLS_LDO_HIX22 is requested using ‘%tldo_hix22’.
R_SPARC_TLS_LDO_LOX10 is requested using ‘%tldo_lox10’.
R_SPARC_TLS_LDO_ADD is requested using ‘%tldo_add’.
R_SPARC_TLS_IE_HI22 is requested using ‘%tie_hi22’.
R_SPARC_TLS_IE_LO10 is requested using ‘%tie_lo10’.
R_SPARC_TLS_IE_LD is requested using ‘%tie_ld’.
R_SPARC_TLS_IE_LDX is requested using ‘%tie_ldx’.
R_SPARC_TLS_IE_ADD is requested using ‘%tie_add’.
R_SPARC_TLS_LE_HIX22 is requested using ‘%tle_hix22’.
R_SPARC_TLS_LE_LOX10 is requested using ‘%tle_lox10’.

Here are some example TLS model sequences.

First, General Dynamic:

sethi  %tgd_hi22(symbol), %l1
add    %l1, %tgd_lo10(symbol), %l1
add    %l7, %l1, %o0, %tgd_add(symbol)
call   __tls_get_addr, %tgd_call(symbol)
nop

Local Dynamic:

sethi  %tldm_hi22(symbol), %l1
add    %l1, %tldm_lo10(symbol), %l1
add    %l7, %l1, %o0, %tldm_add(symbol)
call   __tls_get_addr, %tldm_call(symbol)
nop
sethi  %tldo_hix22(symbol), %l1
xor    %l1, %tldo_lox10(symbol), %l1
add    %o0, %l1, %l1, %tldo_add(symbol)

Initial Exec:

sethi  %tie_hi22(symbol), %l1
add    %l1, %tie_lo10(symbol), %l1
ld     [%l7 + %l1], %o0, %tie_ld(symbol)
add    %g7, %o0, %o0, %tie_add(symbol)
sethi  %tie_hi22(symbol), %l1
add    %l1, %tie_lo10(symbol), %l1
ldx    [%l7 + %l1], %o0, %tie_ldx(symbol)
add    %g7, %o0, %o0, %tie_add(symbol)

And finally, Local Exec:

sethi  %tle_hix22(symbol), %l1
add    %l1, %tle_lox10(symbol), %l1
add    %g7, %l1, %l1

When assembling for 64-bit, and a secondary constant addend is specified in an address expression that would normally generate an R_SPARC_LO10 relocation, the assembler will emit an R_SPARC_OLO10 instead.