RISCV instructions
I am new to riscv and I am confused between la and lw.
I know that la stands for load address and lw stands for load word. If address of VAL is 0x100 and data value of VAL is 0x11 should x3 stores 0x100 and x4 stores 0x11?
la x7, VAL
sw x3, 0(x7)
lw x4, VAL
bne x4, x3
riscv
edited Nov 21 at 10:37
FabienM
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
add a comment |
I am new to riscv and I am confused between la and lw.
I know that la stands for load address and lw stands for load word. If address of VAL is 0x100 and data value of VAL is 0x11 should x3 stores 0x100 and x4 stores 0x11?
la x7, VAL
sw x3, 0(x7)
lw x4, VAL
bne x4, x3
riscv
edited Nov 21 at 10:37
FabienM
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
add a comment |
I am new to riscv and I am confused between la and lw.
I know that la stands for load address and lw stands for load word. If address of VAL is 0x100 and data value of VAL is 0x11 should x3 stores 0x100 and x4 stores 0x11?
la x7, VAL
sw x3, 0(x7)
lw x4, VAL
bne x4, x3
riscv
edited Nov 21 at 10:37
FabienM
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
I am new to riscv and I am confused between la and lw.
I know that la stands for load address and lw stands for load word. If address of VAL is 0x100 and data value of VAL is 0x11 should x3 stores 0x100 and x4 stores 0x11?
la x7, VAL
sw x3, 0(x7)
lw x4, VAL
bne x4, x3
riscv
riscv
edited Nov 21 at 10:37
FabienM
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
edited Nov 21 at 10:37
FabienM
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
edited Nov 21 at 10:37
FabienM
1,076725
edited Nov 21 at 10:37
FabienM
1,076725
edited Nov 21 at 10:37
FabienM
1,076725
1,076725
asked Nov 21 at 5:17
YoungBin Jo
92
asked Nov 21 at 5:17
YoungBin Jo
92
asked Nov 21 at 5:17
YoungBin Jo
92
92
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
la computes an pointer-sized effective address, but does not perform any memory access. The effective address itself is what is loaded into x7.
(Also note that la is a pseudo instruction that may expand into two instructions, depending on VAL — none the less, the sequence computes an effective address and that is its result (no memory access is performed).)
lw also computes an effective address; however, it uses the effective address in a word-sized memory access, and the result of that memory access is the value loaded into x4.
lb would do the same as lw except that the memory access is byte-sized.
As far as your code sequence goes, the value that was in x3 (which cannot be determined from your code snippet) will be stored into memory at locations 0x100-0x103 (this is a word-sized store).
The lw will reload the value that was written by the sw. (Note that the lw in this case may also expand to multiple instructions depending on VAL, whereas the sw is a single instruction regardless of VAL.)
The bne (though missing a target label) will not branch.
answered Nov 22 at 16:26
Erik Eidt
2,41011723
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53405655%2friscv-instructions%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
la computes an pointer-sized effective address, but does not perform any memory access. The effective address itself is what is loaded into x7.
(Also note that la is a pseudo instruction that may expand into two instructions, depending on VAL — none the less, the sequence computes an effective address and that is its result (no memory access is performed).)
lw also computes an effective address; however, it uses the effective address in a word-sized memory access, and the result of that memory access is the value loaded into x4.
lb would do the same as lw except that the memory access is byte-sized.
As far as your code sequence goes, the value that was in x3 (which cannot be determined from your code snippet) will be stored into memory at locations 0x100-0x103 (this is a word-sized store).
The lw will reload the value that was written by the sw. (Note that the lw in this case may also expand to multiple instructions depending on VAL, whereas the sw is a single instruction regardless of VAL.)
The bne (though missing a target label) will not branch.
answered Nov 22 at 16:26
Erik Eidt
2,41011723
add a comment |
la computes an pointer-sized effective address, but does not perform any memory access. The effective address itself is what is loaded into x7.
(Also note that la is a pseudo instruction that may expand into two instructions, depending on VAL — none the less, the sequence computes an effective address and that is its result (no memory access is performed).)
lw also computes an effective address; however, it uses the effective address in a word-sized memory access, and the result of that memory access is the value loaded into x4.
lb would do the same as lw except that the memory access is byte-sized.
As far as your code sequence goes, the value that was in x3 (which cannot be determined from your code snippet) will be stored into memory at locations 0x100-0x103 (this is a word-sized store).
The lw will reload the value that was written by the sw. (Note that the lw in this case may also expand to multiple instructions depending on VAL, whereas the sw is a single instruction regardless of VAL.)
The bne (though missing a target label) will not branch.
answered Nov 22 at 16:26
Erik Eidt
2,41011723
add a comment |
la computes an pointer-sized effective address, but does not perform any memory access. The effective address itself is what is loaded into x7.
(Also note that la is a pseudo instruction that may expand into two instructions, depending on VAL — none the less, the sequence computes an effective address and that is its result (no memory access is performed).)
lw also computes an effective address; however, it uses the effective address in a word-sized memory access, and the result of that memory access is the value loaded into x4.
lb would do the same as lw except that the memory access is byte-sized.
As far as your code sequence goes, the value that was in x3 (which cannot be determined from your code snippet) will be stored into memory at locations 0x100-0x103 (this is a word-sized store).
The lw will reload the value that was written by the sw. (Note that the lw in this case may also expand to multiple instructions depending on VAL, whereas the sw is a single instruction regardless of VAL.)
The bne (though missing a target label) will not branch.
answered Nov 22 at 16:26
Erik Eidt
2,41011723
la computes an pointer-sized effective address, but does not perform any memory access. The effective address itself is what is loaded into x7.
(Also note that la is a pseudo instruction that may expand into two instructions, depending on VAL — none the less, the sequence computes an effective address and that is its result (no memory access is performed).)
lw also computes an effective address; however, it uses the effective address in a word-sized memory access, and the result of that memory access is the value loaded into x4.
lb would do the same as lw except that the memory access is byte-sized.
As far as your code sequence goes, the value that was in x3 (which cannot be determined from your code snippet) will be stored into memory at locations 0x100-0x103 (this is a word-sized store).
The lw will reload the value that was written by the sw. (Note that the lw in this case may also expand to multiple instructions depending on VAL, whereas the sw is a single instruction regardless of VAL.)
The bne (though missing a target label) will not branch.
answered Nov 22 at 16:26
Erik Eidt
2,41011723
answered Nov 22 at 16:26
Erik Eidt
2,41011723
answered Nov 22 at 16:26
Erik Eidt
2,41011723
answered Nov 22 at 16:26
Erik Eidt
2,41011723
2,41011723
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53405655%2friscv-instructions%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
